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THE PKHSTCIPLES OF 



ANIMAL NUTRITION. 



WITH SPECIAL REFERENCE TO THE 
NUTRITION OF FARM ANIMALS. 



BY 

HENRY PRENTISS ARMSBY, Ph.D., 

Director of The Pennsylvania State College Agricultural Experiment Station ; 
Expert in Animal Nutrition, United States Department of Agriculture. 



FIRST EDITION. 
FIRST THOUSAND. 



NEW YORK : 

JOHN WILEY & SONS. 

London: CHAPMAN & HALL, Limited. 

1903. 



^ 



THE LIBRARY OF 
CONGRESS, 

Two Copies Received 

FEB 2 1903 

Copyright Entry 

LASS A, XXc, No, 

COPY 8. 




Copyright, 1903, 

BY 

HENRY P. ARMSBY. 



ROBERT DRUMMOND, PRINTER, NEW YORK. 



PREFACE. 



The past two decades have not only witnessed great activity in 
the study of the various problems of animal nutrition, but they are 
especially distinguished by the new point of view from which these 
problems have come to be regarded. Speaking broadly, it may be 
said that to an increasing knowledge of the chemistry of nutrition 
has been added a clear and fairly definite general conception of the 
vital activities as transformations of energy and of the food as 
essentially the vehicle for supplying that energy to the organism. 
This conception of the function of nutrition has been a fruitful 
one, and in particular has tended to introduce greater simplicity and 
unity into thought and discussion. Much exceedingly valuable 
work has been done under its guidance, while it points the way 
toward even more important results in the future. The following 
pages are not a treatise upon stock-feeding, but are an attempt to 
present in systematic form to students of that subject a summary of 
our present knowledge of some of the fundamental principles of ani- 
mal nutrition, particularly from the standpoint of energy relations, 
with special reference to their bearings upon the nutrition of farm 
animals. Should the attempt at systematization appear in some 
instances premature or ill-advised, the writer can only plead that 
even a temporary or tentative system, if clearly recognized as such, 
may be preferable to unorganized knowledge. The scaffolding 
has its uses, even though it form no part of the completed building. 

The attentive reader, should there be such, will not fail to note 
that the work is limited to those aspects of the subject included 
under the more technical term of "The Statistics of Nutrition/' 
and that even in this restricted field some important branches of 
the subject have been omitted on account of what has seemed to 



iv PREFACE. 

the writer a lack of sufficient accurate scientific data for their profit- 
able discussion. Moreover, many principles which are already 
familiar have been considered rather cursorily in order to allow a 
more full treatment of less well-known aspects of the subject, even 
at the expense of literary proportion. 

The substance of this volume was given in the form of lectures 
before the Graduate Summer School of Agriculture at the Ohio 
State University in 1902, and has been prepared for publication at 
the request of instructors and students of that school. In thus 
presenting it to a somewhat larger public the author ventures to 
hope that it may tend in some degree to promote the rational study 
of stock-feeding and to aid and stimulate systematic investigation 
into both its principles and practice. 

State College, Pa., November, 1902. 



CONTENTS. 



PAGE 

Introduction 1 

The Statistics of Nutrition 3 

PART I. 
THE INCOME AND EXPENDITURE OF MATTER. 

CHAPTER I. 

The Food 5 

CHAPTER II. 

Metabolism 14 

§ 1. Carbohydrate Metabolism 17 

§ 2. Fat Metabolism 29 

§ 3. Proteid Metabolism 38 

Anabolism 38 

Katabolism 41 

The Non-proteids 52 

CHAPTER III. 

Methods of Investigation 59 

CHAPTER IV. 

The Fasting Metabolism 80 

§ 1. The Proteid Metabolism 81 

§ 2. The Total Metabolism 83 

CHAPTER V. 

The Relations of Metabolism to Food-supply 93 

§ 1. The Proteid Supply 94 

Effects on Proteid Metabolism 94 

Effects on Total Metabolism 104 

Formation of Fat from Proteids 107 

v 



Vi CONTENTS. 

PAOE 

§ 2. The Non-nitrogenous Nutrients 114 

Effects on Proteid Metabolism 1 14 

The Minimum of Proteids 133 

Effects on Total Metabolism 144 

Mutual Replacement of Nutrients 148 

Utilization of Excess — Sources of Fat 162 

CHAPTER VI. 

The Influence of Muscular Exertion upon Metabolism 185 

§ 1. General Features of Muscular Activity 185 

Muscular Contraction 185 

Secondary Effects of Muscular Exertion 191 

J 2. Effects upon Metabolism 193 

Upon the Proteid Metabolism 194 

Upon the Carbon Metabolism 209 



PART II. 

THE INCOME AND EXPENDITURE OF ENERGY. 

CHAPTER VII 
Force and Energy. 226 

CHAPTER VIII. 
Methods of Investigation 234 

CHAPTER IX. 
The Conservation of Energy in the Animal Body 258 

CHAPTER X. 

The Food as a Source of Energy — Metabolizable Energy 269 

§ 1. Experiments on Carnivora 272 

§ 2. Experiments on Man 277 

§ 3. Experiments on Herbivora 281 

Metabolizable Energy of Organic Matter 284 

Total Organic Matter 285 

Digestible Organic Matter 297 

Energy of Digestible Nutrients 302 

Gross Energy 302 

Metabolizable Energy 310 



CONTENTS. 



CHAPTER XI. 

PAGE 

Internal Work 336 

§ 1. The Expenditure of Energy by the Body 336 

§ 2. The Fasting Metabolism 340 

Nature of Demands for Energy 340 

Heat Production 344 

Influence of Thermal Environment 347 

Influence of Size of Animal 359 

§ 3. The Expenditure of Energy in Digestion and Assimilation 372 

CHAPTER XII. 

Net Available Energy — Maintenance 394 

§ 1. Replacement Values 396 

§ 2. Modified Conception of Replacement Values 405 

§ 3. Net Availability 412 

Determinations of Net Availability 413 

Discussion of Results 430 

Influence of Amount of Food 430 

Character of Food . . 431 

The Maintenance Ration 432 

CHAPTER XIII. 

The Utilization of Energy 444 

§ 1. Utilization for Tissue Building 448 

Experimental Results . 448 

Discussion of Results 465 

Influence of Amount of Food 466 

Influence of Thermal Environment 471 

Influence of Character of Food , . . 472 

The Expenditure of Energy in Digestion, Assimilation 

and Tissue Building . . 491 

§ 2 Utilization for Muscular Work 494 

Utilization of Net Available Energy 497 

The Efficiency of the Animal as a Motor 498 

, Conditions determining Efficiency , 511 

Utilization of Metabolizable Energy 525 

Wolff's Investigations 528 



THE PRINCIPLES OF ANIMAL NUTRITION, 



INTRODUCTION. 

The body of an animal, regarded from a chemical point of view, 
consists of an aggregate of a great variety of substances, of which 
water, protein, and the fats, with smaller amounts of certain 
carbohydrates, largely predominate. By far the greater portion of 
the substance of the body, aside from its water, consists of so- 
called " organic " compounds; i.e., compounds of carbon with hydro- 
gen, oxygen, nitrogen, and, to a smaller extent, with sulphur and 
phosphorus. These compounds are in many cases very complex, 
and all of them have this in common, that they contain a con- 
siderable store of potential energy. 

It is through these complex " organic " compounds that the phe- 
nomena of life are manifested. All forms of life with which we are 
acquainted are intimately associated with the conversion of com- 
plex into simpler compounds by a series of changes which, regarded 
as a whole, partake of the nature of oxidations. During this break- 
ing down and oxidation more or less of the potential energy of these 
compounds is liberated, and it is this liberation of energy which is 
the essential end and object of the whole process and which, if not 
synonymous with life itself, is the objective manifestation of life. 
This is equally true of the plant and the animal, although masked 
in the case of green plants by the synthetic activity of the chloro- 
phyl in the presence of light. The process is most manifest in the 
animal, however, both on account of the inability of the latter to 
utilize the radiant energy of the sun and on account of the greater 
intensity of the process itself. 

Setting aside for the moment any storing up of material, and 



2 PRINCIPLES OF ANIMAL NUTRITION. 

therefore of potential energy, in the body for the future use of the 
animal itself or of its offspring as being, from a physiological point of 
view, temporary and incidental, the sole useful product of the animal 
is energy. All the physical effect which we can produce, either 
through our own bodies or those of our domestic animals, is simply 
to move something, and moving something is equivalent to the 
exertion of energy. This motion may be the motion of visible 
masses of matter in the performance of useful work or the invisible 
molecular motion of heat, which is economically a waste product, 
but in either case the animal is a source of energy which is imparted 
to its surroundings. From this point of view, then, we may look ' 
upon the animal as a mechanism for transforming the stored-up 
energy of the sun's rays, contained in its tissues, into the active or 
" kinetic " forms of heat and motion. The various cells and tissues 
of the living animal body, in the performance of their several func- 
tions, break down and oxidize the proteids, fats, carbohydrates , 
and other materials of which they are composed or which are con- 
tained in them, seizing, as it were, upon the energy thus liberated 
and converting it, here into heat, there into motion, again into the 
energy of chemical change, as the needs of the organism demand. 

The very definition of physical life, then, implies that the living 
animal is constantly consuming its own substance, rejecting the 
simpler compounds which result and giving off energy in the various 
forms characteristic of living beings. Obviously, this process, if 
unchecked, would soon lead to the destruction of the organism and 
the dissipation of its store of potential energy. To prevent this 
catastrophe is the object of the great function of nutrition. 

This function, in its broader outlines, is familiar to us all through 
daily experience and observation. The living animal requires to 
be frequently supplied with certain substances which collectively 
constitute its food. This food contains a great variety of chemical 
ingredients, but much the larger part of it consists of "organic" 
compounds belonging to the three great groups already noted as 
making up the larger share of the organic matter of the body, viz., 
the proteids, the fats, and especially the carbohydrates, and while 
the individual members of these groups differ in the two cases, the 
ingredients of the food, like those of the body, contain a large store 
of potential energy. These and other "organic" substances, 



INTRODUCTION. 3 

together with more or less mineral matter, are separated by the 
organism, in the processes of digestion and resorption, from the un- 
essential or unavailable matters of the food. The latter are rejected 
from the body, while the former are used by it to take the place 
of the material broken down and excreted by its vital activities, 
and thus serve to maintain its capital of matter and of potential 
energy. 

In other words, the food may be regarded as the vehicle by 
means of which a little portion of the " infinite and eternal energy 
from which all things proceed " is put for the time being at the 
service of the individual ; as being not so much a supply of matter 
to make good the waste of tissue as a supply of energy for the mani- 
festations of life. 

The animal body, then, from our present standpoint, consists of 
a certain amount of matter which has been temporarily segregated 
from the rest of the universe and which represents a certain store 
or capital of potential energy. This aggregate of matter and 
energy is in a constant state of change or flux. On the one hand, 
its vital activities are continually drawing upon its capital. By 
the very act of living it expends matter and energy. On the other 
hand, by means of the function of nutrition, it is continually receiv- 
ing supplies of matter and energy from its environment and adding 
them to its capital. Plainly, then, the growth, the maintenance, or 
the decay of the body depends upon the relation which it is able to 
maintain between the income and the expenditure of matter and 
energy. If the two are equal, the animal is simply maintained 
without increase or decrease; if the income is greater than the 
expenditure, the body adds to its capital of matter and energy, if 
the income is less than the expenditure, the necessary result is a 
diminution in the accumulated capital which, if continued, must 
ultimately result in death. 

We thus reach an essentially statistical standpoint, and this 
aspect of the subject of nutrition, which has been designated by 
some writers as "The Statistics of Nutrition," forms the subject of 
the succeeding pages. The topic naturally divides itself into two 
distinct although closely related parts, viz. : 

1. The income and expenditure of matter. 

2. The income and expenditure of energy. 



4 PRINCIPLES OF ANIMAL NUTRITION. 

These topics will be considered in the above order, it being 
assumed that the reader is already familiar with the general nature 
of the nutritive processes included under the general heads of 
digestion, resorption, circulation, respiration, and excretion. 



PART I. 
THE INCOME AND EXPENDITURE OF MATTER. 



CHAPTER I. 
THE FOOD. 

The supply of matter to the body is, of course, contained in the 
food, including water and the oxygen taken up from the air. In' 
a more limited and familiar sense, the term food is employed to 
signify the supply of solid matter, or dry matter, to the animal. 
It is proposed here simply to recall certain familiar facts relative 
to the composition and digestibility of the food in this narrower 
sense, taking up the subject in the barest outline. 

Composition. — While a vast number of individual chemical 
compounds are found in common feeding-stuffs, the conventional 
scheme for their analysis unites these substances into groups and 
regards feeding-stuffs as composed, aside from water and mineral 
matter, essentially of protein, carbohydrates and related bodies, 
and fats. Or, setting aside the mineral ingredients, the " organic " 
ingredients may be divided into the nitrogenous, comprised under 
the term protein, and the non-nitrogenous, including the fats and 
carbohydrates. 

Protein. — The name "protein" originated with Mulder, who 
used it to designate what he supposed to be a common ingredient 
of all the various proteids, but it has since come to be employed as a 
group name for the nitrogenous ingredients both of feeding-stuffs 
and of the animal body. 

The amount of protein in feeding-stuffs we have at present no 

5 



6 RINCIPLES OF ANIMAL NUTRITION. 

means of determining directly, but it is commonly estimated from 
the amount of nitrogen upon two assumptions: first, that all the 
substances of the protein group contain 16 per cent, of nitrogen, and 
second, that all the nitrogen of feeding-stuffs exists in the proteid 
form. On the basis of these assumptions, protein is, of course, 
equal to total nitrogen X 6.25. 

Although it was never claimed that this method of estimating 
protein was strictly accurate, it was for a long time assumed that 
the two sources of error involved were not serious. Later investi- 
gations, however, have dispelled this pleasing illusion. Further 
investigations of the true proteids, notably those of Ritthausen and 
of Osborne, have shown a very considerable variation in the per- 
centage of nitrogen contained in them, while, on the other hand, the 
researches of Scheibler, E. Schulze, Kellner, and others have shown 
the presence in many feeding-stuffs of relatively large amounts of 
nitrogenous matters of non-proteid nature. The results of these 
latter investigations have made it necessary to subdivide the total 
nitrogenous matter of feeding-stuffs into two groups, called respec- 
tively "proteids" and "non-proteids," while the name "protein" 
has been retained in the sense of total nitrogen X 6.25 or other con- 
ventional factor. For various classes of human foods, Atwater and 
Bryant * propose the following factors, based on the results in- 
dicated in the next two paragraphs, for the computation of protein 
from nitrogen: 

Animal foods 6 . 25 

Wheat, rye, barley, and their manufactured products 5.70 
Maize, oats, buckwheat and rice, and their manufactured 

products 6 . 00 

Dried seeds of legumes 6 . 25 

Vegetables , . , 5 . 65 

Fruits 5.80 

Proteids. — In the absence of any adequate knowledge regarding 
the very complex molecular structure of the proteids, both the 
classification and the terminology of these bodies are in a very con- 
fused state. For convenience, however, we may adopt here those 

* Storrs (Conn.) Ag. Ex. St., Rep. 12, 79. 



THE FOOD. 



tentatively recommended by the Association of American Agri- 
cultural Colleges and Experiment Stations,* viz. : 



( Albumins, 
f Simple -< Globulins, 
C Albuminoids \ and allies - 



Pr a°S g eo^l a ' f ***«• I M ° diM \ SoTplod. 

pounds J [ Collagens or gelatinoids 

I at ~„„«.,.:,i„ i Extractives, 

[ Non -P roteids | Amides, amido-acids, etc. 

It is not necessary for our present purpose to enter into any dis- 
cussion either of the properties of the proteids as a whole or of the 
differences between the different classes of proteids. One point, 
however, is of particular importance, namely, the elementary com- 
position of these bodies. As noted above, this has been found to be 
more variable than was supposed earlier. In particular the per- 
centage of nitrogen has been found to have a somewhat wide range. 
"Recent investigations with perfected methods show percentages 
of nitrogen in the numerous single proteid substances found in the 
grains ranging from 15.25 to 18.78. These are largest in certain 
oil seeds and lupines and smallest in some of the winter grains. 
Ritthausen,f a prominent German authority, concedes that the 
factor 6.25 should be discarded, and suggests the use of 5.7 for the 
majority of cereal grains and leguminous seeds, 5.5 for the oil and 
lupine seeds, and 6.00 for barley, maize, buckwheat, soja-bean, and 
white bean (Phaseolus) rape, and other brassicas. Nothing short 
of inability to secure greater accuracy justifies the longer contin- 
uance of a method of calculation which is apparently so greatly 
erroneous." (Jordan.) 

Non-proteids. — This term is used as a convenient designation 
for all the nitrogenous materials of feeding-stuffs which are not 
proteid in their nature. It is an abbreviated form of non-pro teid 
nitrogenous bodies. The substances of this class found in plants 
are chiefly the organic bases, amides, amido-acids, and similar 
bodies which are produced by the cleavage of the proteid molecule 
under the action of digestive and other ferments or of hydrating 
agents. They appear to exist in the plant partly as intermediate 
stages in the synthesis of the proteids and partly as products of 

*U. S. Dept. Agr., Office of Experiment Station, Bui., 65, p. 117. 
fLandw. Vers. Stat., 74, 391. 



8 PRINCIPLES OF ANIMAL NUTRITION. 

their subsequent cleavage in the metabolism of the plant. They 
are chiefly soluble, crystalline bodies. The most common of them 
is asparagin, which has been, to a certain extent, regarded as 
typical of the group. 

The non-proteids are commonly determined by determining as 
accurately as possible the non-proteid nitrogen and multiplying the 
latter by the factor 6.25. In the case of asparagin, however, which 
contains 21.2 per cent, of nitrogen, the proper factor obviously 
should be 4.7, while the factor would vary for the different forms of 
non-proteids which have been observed in plants. It is no simple 
matter, therefore, either to determine directly the amount of non- 
proteids or to decide upon the proper nitrogen factor in any partic- 
ular case. For the present, however, the factor 4.7 would seem 
to be at least a closer approximation to the truth than 6.25. 

In the animal body the group of non-proteids is represented by 
the so-called "extractives" or "flesh bases" of the muscle, chiefly 
creatin and creatinin. 

jr ATS . — The fats of the plant, like those of the animal, consist 
chiefly of glycerin compounds of the so-called "fatty acids," or of 
similar bodies. These are accompanied in the plant, however, by 
other materials— wax, chlorophyl, etc.— which are extracted along 
with the fat by the common method of determination and consti- 
tute part of the "crude fat" or "ether-extract." The results, 
therefore, which have been obtained in feeding experiments with 
pure fats cannot be used with safety as a basis for estimating the 
nutritive value of the so-called " fat " of feeding-stuffs, particularly 
in the case of coarse fodders. 

Carbohydrates.— The well - characterized group of carbo- 
hydrates makes up a large proportion of the organic matter of our 
more common feeding-stuffs. This group of substances may be sub- 
divided on the basis of molecular structure into hexosans and their 
derivatives (hexoses, bioses, trioses, etc.), on the one hand, whose 
molecules contain six atoms of carbon or a multiple of that number, 
and the pentosans and pentoses, or five-carbon series, on the other. 
In the grains and other common concentrated feeding-stuffs, and 
particularly in the food of man, the hexose group largely predomi- 
nates, including starch, dextrin, the common sugars, and more or 
less cellulose. In the coarse fodders consumed by our domestic 



THE FOOD. 9 

herbivorous animals, while the hexose group is also largely repre- 
sented it is accompanied by no inconsiderable quantities of carbo- 
hydrates belonging to the pentose group. The individual members 
of this latter group are both less abundant and less well known 
chemically than the hexoses, and at present our knowledge of their 
actual nutritive value is somewhat scanty. Since the methods for 
their determination are based upon the fact that they yield furfural 
upon boiling with dilute hydrochloric acid, some recent analysts 
have proposed the term " furfuroids " as a more appropriate desig- 
nation of these substances as determined by present methods. 

In the conventional scheme for the analysis of feeding-stuffs, the 
carbohydrates are subdivided, not upon the basis of their chemical 
structure but upon the basis of their solubility. Those members 
of the group which can be brought into solution by boiling dilute 
acids and alkalies under certain conventional conditions are grouped 
together as "Nitrogen-free extract," while those ingredients 
which resist solution under these conditions are designated as 
"Crude fiber." The more common hexose carbohydrates, such as 
starch, sugars, etc., are included in the nitrogen-free extract, while 
the larger part, although not all, of the cellulose is included under 
the crude fiber. At the same time, more or less of the pentose carbo- 
hydrates or " furfuroids " are found in both these groups, while the 
crude fiber of coarse fodders contains also a variety of other ill- 
known compounds, somewhat roughly grouped together under the 
general designation of ligneous material. 

Digestibility.— A part of nearly all common food materials is 
incapable of digestion and is rejected in the feces. In the food of 
man and that of carnivorous animals this indigestible portion is 
usually small and may disappear entirely. In the food of herbivora, 
on the other hand, there are contained relatively large amounts of 
substances which are incapable of solution in the digestive tract, 
while varying proportions of materials which in themselves are 
capable of being digested may escape actual digestion under some 
circumstances. In the latter animals, therefore, it becomes par- 
ticulary important to determine the digestible portion of the food. 
The digestibility of a feeding-stuff is estimated indirectly by deter- 
mining as accurately as possible the undigested matter eliminated 
from the body in the feces and subtracting it from the total amount 



io PRINCIPLES OF ANIMAL NUTRITION. 

contained in the food. This method may of course be applied 
either to the dry matter or the organic matter of the food as a 
whole or to any single determinable ingredient. 

Metabolic Products. — The digestive tract of an animal, how- 
ever, not only serves as a mechanism for the digestion of food but 
has excretory functions as well, and the rejected matter contains, 
besides the undigested portion of the food, these excreta and the 
metabolic products of intestinal action. In the case of food largely 
or completely digestible, these substances may make up the larger 
portion or even the whole of the feces, while, on the other hand, 
they constitute but a small proportion of the bulky, excreta of 
herbivora. 

It is obvious that these products must be taken account of if it is 
desired to learn the actual digestibility of the food. Unfortunately, 
however, we have at present no trustworthy method for their deter- 
mination. In the past it has been customary to designate the 
difference between food and feces as digestible and, in the case of 
domestic animals at least, to assume that the error involved is not 
serious. 

Apparent Digestibility — Availability. — Even with herbivo- 
rous animals, however, the presence of the so-called metabolic 
products in the feces may give rise to serious errors in the deter- 
mination of the real digestibility of some ingredients of the food, 
notably fat and protein. With carnivora, or with the human 
subject, the case is for obvious reasons still worse, and it is 
scarcely possible to determine the digestibility of the food in the 
strict sense of the word. 

The difference between food and feces does represent, however, 
the net gain of matter to the organism resulting from the digestion 
of the food. To express this conception, the use of the word avail- 
able has been proposed by Atwater.* The " available nutrients " of 
a food, according to him, are the actually digestible nutrients minus 
the metabolic products contained in the feces and which may be 
regarded as representing the expenditure of matter, in the form of 
residues of digestive fluids, intestinal mucus, epithelium, etc., 
necessarily incident to the digestion of the food. The term has been 

* Storrs (Conn.) Agr'] Expt. St., Rep., 12, 69. 



THE FOOD. ii 

used chiefly in connection with human nutrition. In discussions of 
animal nutrition the terms digestible and digestibility have become 
so firmly established that it may be questioned whether the intro- 
duction now of a new term would not create more confusion than it 
would prevent, and whether it is not preferable, when strict accuracy 
of expression is required, to attach a modifying word and designate 
the difference between food and feces as apparently digestible, in 
distinction from the real digestibility, which we cannot as yet deter- 
mine. 

Determination of Apparent Digestibility. — The determi- 
nation of the apparent digestibility of the nutrients of a feeding- 
stuff in the above sense, or of their " digestibility " in the older sense, 
consists simply in determining the amount of the feces or of their 
separate ingredients and comparing them with the correspond- 
ing amounts in the food. 

Aside from ordinary analytical precautions, the chief condition 
of accurate results is that the feces correspond to the food consumed. 
In animals with a comparatively simple digestive canal, like man 
and the carnivora, this is readily brought about by the ingestion of 
a small amount of some substance like powdered charcoal or infu- 
sorial earth, which is in itself indigestible and which serves to sepa- 
rate the feces of two successive periods. In the case of herbivora, 
on the other hand, the undigested residues of the food become mixed 
to a large extent with those of the previous period. In this case, 
therefore, it is essential that a preliminary feeding be continued for 
a sufficient length of time to remove the residues of previous foods 
from the digestive organs, and further that the experiment itself 
extend through a number of days in order to eliminate the 
influence of irregularity of excretion. 

Significance of Results. — It is plain from what has just 
been said that what the results of such an experiment actually 
show is that a certain amount of material has disappeared from 
the food during its transit through the alimentary canal. This 
fact of itself, however, does not necessarily show that the missing 
material has been digested in any true sense. In the case of animals 
possessing a relatively short and simple digestive apparatus, we are 
probably justified in assuming that the difference between food and 
undigested matter represents material that has actually been 



12 PRINCIPLES OF ANIMAL NUTRITION. 

digested. In the long- and complicated digestive apparatus of 
herbivora, however, there is the possibility that a variety of proc- 
esses may go on aside from a simple solution of nutrients by the 
digestive fluids. In particular, it has been shown, as will appear in 
greater detail later, that extensive fermentations, particularly of the 
carbohydrates, occur, and that relatively large amounts of these 
bodies may be destroyed in this way. 

Furthermore, with our present conventional scheme for fodder 
analysis, we have to take account of the possibility of the conversion 
of members of one group of nutrients into those of another. For 
example, it seems not improbable that a portion of the crude fiber 
of feeding-stuffs may be so modified in the digestive tract, without 
being actually dissolved, that, in the feces, it is determined as 
nitrogen-free extract, thus diminishing the apparent digestibility 
of the latter group and increasing that of the crude fiber.* 

Composition of Digested Food. — The proteids during the 
process of digestion are largely converted into proteoses and pep- 
tones, while the trypsin of the pancreatic juice, at least outside the 
body, carries the cleavage of the proteid molecule still further and 
gives rise to comparatively simple, crystalline bodies. It is not 
altogether clear to what extent this degradation of the proteids 
occurs in natural digestion, but the probability appears to be that 
it does not play a large part, and it has been generally believed that 
the proteids are resorbed chiefly as proteoses and peptones. 

The non-proteids being largely crystalline bodies and readily 
soluble, we may presume that they are resorbed without material 
change except so far as they may serve as nitrogenous food for the 
micro-organisms of the digestive tract. 

The fat of the food does not undergo any profound change in 
digestion, but appears to be resorbed largely in the form of an 
emulsion. A part of it, however, is undoubtedly saponified by 
the bile, although the extent to which this process takes place is a 
disputed point, while in some cases at least a cleavage into glycerin 
and free fatty acids appears to take place. 

The carbohydrates, particularly the easily soluble members of 
the hexose group, are in the case of man and the carnivora, and 

*Cf. Fraps, Jour. Am. Chem. Soc, 22, 543. 



THE FOOD. 13 

probably also to a large extent in the swine and horse, converted 
into sugars and resorbed in that form. 

Fermentations. — Reference has already been made to the fermen- 
tations taking place in the digestive tract. In the herbivora, and 
especially in ruminants, these fermentations play an important 
part in the solution of the carbohydrates which make up so large 
a portion of the food of these animals. These bodies undergo a 
fermentation which was first studied by Tappeiner * in the case of 
cellulose, but which has since been shown by G. Kiihn f to extend 
also to the more soluble carbohydrates. The products of this 
fermentation appear to be methane, carbon dioxide, and organic 
acids, chiefly, according to Tappeiner, acetic and butyric. Of these 
products, only the organic acids at best can be supposed to be of 
any value to the animal organism, and obviously it makes a very 
serious difference in our estimate of the nutritive value of starch, 
for example, whether it is resorbed chiefly or entirely in the form of 
sugar or whether in a ruminant more than half of it, as in some of 
Kiihn's experiments, is fermented. 

* Zeit. f. Biol, 20, 52. f Landw. Vers. Stat., 44, 569. 



CHAPTER II. 
METABOLISM. 

General Conception. — By the various processes of digestion 
and resorption the epithelium of the alimentary canal extracts from 
the crude materials eaten those ingredients which are fitted to 
nourish the animal and transmits them more or less directly to the 
general circulation which carries them to all the tissues of the body. 
While these ingredients are many in number and diverse in charac- 
ter, yet the vast mass of them, aside from the water in which most 
of them are dissolved, may be grouped under six heads, viz., ash 
ingredients, albuminoids or bodies related to the albuminoids, 
amides and other crystalline nitrogenous substances, fats, carbo- 
hydrates, and organic acids, and these, together with relatively 
small amounts of other materials, may be regarded as constituting 
the real food of the organism. 

As was pointed out in the Introduction, the cells of which the 
living tissues of the animal body are composed are the seat of con- 
tinual chemical change. On the one hand, the digested ingredients 
of the food which are brought to them by the circulation are being 
built up into the structure of the body. On the other hand, the 
material of the cells is undergoing a continual process of breaking 
down and oxidation, uniting with the oxygen supplied by the blood 
to form the waste products which are removed from the body 
through the organs of excretion. These excretory products are 
substantially carbon dioxide, water, and urea and similar nitroge- 
nous substances. 

The general term Metabolism is commonly used to designate the 
totality of the chemical and physical changes which the materials 
of the resorbed food, or of the tissues formed from them, undergo in 
being converted into the excretory products. Similarly, we may 
speak in a more restricted sense of the metabolism of a single ingre- 

14 



METABOLISM. 15 

dient of the food, as of the proteids, carbohydrates, or fats. Thus 
proteid metabolism signifies the chemical changes undergone by the 
proteids of the food in their conversion into the corresponding 
excretory products. In ordinary usage the chemical reactions 
undergone by the ash ingredients of the food are not included, the 
word metabolism being practically used to designate the chemical 
changes in the organic matter of food or tissue. 

Metabolism a Process of Oxidation. — The process of met- 
abolism as a whole is one of oxidation. While we must beware 
of being misled by analogy into regarding as a simple burning of 
food-materials that which is in reality a highly complex action of 
the living cells of the organism, still the final result is much the 
same in both cases. Starting with more or less complex organic 
substances and oxygen, we end either with the completely oxidized 
compounds carbon dioxide and water or with nitrogenous sub- 
stances like urea more highly oxidized than the protein from which 
they are derived. 

The oxidative character of the total metabolism is most simply 
illustrated by a comparison of the percentage of oxygen contained 
in the most prominent ingredients of the food, on the one hand, and 
in the chief excretory products, on the other hand, as in the follow- 
ing statement: 

Percentage of Oxygen. 
In food: 

Protein (average) 23.00 

Fats 11.50 

Dextrose 53 . 33 

In excreta: 

Urea 26.67 

Carbon dioxide 72 . 72 

Water 88.89 

Metabolism an Analytic Process. — From a slightly different 
point of view, metabolism may be described as an analytic process. 
The molecules of the food constituents are highly complex. The 
molecule of dextrose or lsevulose, the forms in which the carbo- 
hydrates are chiefly resorbed, contains 24 atoms; the molecules of 



1 6 PRINCIPLES OF ANIMAL NUTRITION. 

the three most common fats, respectively 155, 167, and 173 atoms. 
The molecular structure of the proteids has not yet been made out, 
but it is highly complex.* The molecules of the excretory prod- 
ucts, on the contrary, are comparatively simple, those of carbon 
dioxide and water containing but three atoms each, that of urea 
eight, and even that of hippuric acid but twenty-two. 

In metabolism, in other words, the complex molecules of the 
carbohydrates, fats, proteids, etc., which have been built up in the 
plant, by means of the energy contained in the sun's rays, out of 
carbon dioxide, water, and nitric acid or ammonia, gradually break 
down again into simpler compounds, their atoms reuniting with 
the oxygen from which they were separated in the plant. 

Metabolism a Gradual Process. — The chemical changes in- 
cluded under the term metabolism take place gradually. As has 
already been indicated, metabolism is not a simple oxidation of 
nutrients, like the burning of fuel in a stove, but the nutrients enter, 
to a large extent at least, into the structure of the cells of which the 
various tissues are composed. Metabolism is really the sum of the 
chemical actions through which the nutrition and life of these cells 
is manifested. These actions, however, differ from tissue to tissue 
and from cell to cell, and even in the same cell from time to time, 
and the resulting metabolic products are correspondingly varied. 
Between the nutrients supplied to the cells by the blood and the 
final products of metabolism as excreted from the body there are 
innumerable intermediate products, a few of which we know but 
concerning most of which we are still ignorant. We know the first 
and last terms of the series and thus are able to measure, as it 
were, the algebraic sum of the changes, but of the single factors 
making up this sum. as well as of the specific tissues concerned in 
the changes, we are largely ignorant, although we know that they 
are numerous. 

Anabolism and Katabolism. — While the process of metab- 
olism as a whole is one of analysis and oxidation, with liberation 
of energy, it must not be supposed that each single step in the 
process is of this nature. As has been already pointed out, the 
chemical activities of the tissues possess a dual character. By the 

* Osborne (Zeit. physiol. Chem., 33, 240) has recently obtained the 
number 14,500 as the approximate molecular weight of edestin. 



METABOLISM. 17 

various processes of nutrition, ingredients of the food are first incor- 
porated into the tissues of the body, to be subsequently broken 
down and oxidized. In this building-up process changes undoubt- 
edly occur in the direction of greater complexity of molecular struc- 
ture, involving the temporary absorption of energy. Thus it is 
known that fats may be formed from carbohydrates in the body. 
Many physiologists hold that the metabolism in the quiescent muscle 
results in the building up of a complex " contractile substance, " 
whose breaking down furnishes the energy for muscular work. In 
general, we may regard it as highly probable that the molecules of 
the living substance of the body are much more complex than those 
of the nutrients of the food, and that the former are built up out of 
the latter by synthetic processes, carried on at the expense of energy 
derived from the breaking down of other molecules. Such changes 
as this are called anabolic and the process anabolism, while the 
changes in the direction of greater simplicity of molecular structure 
are called katabolic, and the process katabolism. The metabolism 
of the living body, then, consists of both anabolism and katabolism. 
By the former the food nutrients are built up into body material; 
by the latter they are broken down, yielding finally the compara- 
tively simple excretory products. On the whole, however, the 
katabolism prevails over the anabolism, so that metabolism as a 
whole is, as already stated, an analytic and oxidative process. 
Neither the anabolism of tissue production nor the minor anabolic 
changes which seem to occur in various tissues alter the main direc- 
tion of the metabolic changes in the body, but, from the standpoint 
of the statistics of nutrition, are simply eddies in the main current 

§ 1. Carbohydrate Metabolism. 

HEXOSE CARBOHYDRATES. 

The hexose carbohydrates of the food appear to be resorbed 
chiefly by the capillary blood-vessels of the intestines. For the 
most part, they reach the blood in the form of dextrose, with smaller 
amounts of lsevulose and with greater or less quantities of acetic, 
butyric, lactic, and other acids derived chiefly from the fermenta- 
tion of the carbohydrates in the digestive tract. In the general 
circulation only dextrose is found. 



1 8 PRINCIPLES OF ANIMAL NUTRITION. 

The percentage of dextrose in the blood is small, but remarkably 
constant, the limits of variation being from about 0.11 to about 0.20 
per cent., and the average about 0.15 per cent. Its amount 
varies but slightly in different regions of the body, and in different 
classes of animals, and is scarcely at all affected by the nature or 
amount of the food. Not only so, but any excess of dextrose in the 
blood is promptly gotten rid of. It is a striking fact that if any con- 
siderable amount of this substance, which forms so large a part of 
the resorbed nutriment, be injected directly into the blood it is 
treated as an intruder and at once excreted through the kidneys. 
Evidently it is of the greatest importance to the organism that the 
supply of this substance to the tissues shall be constant. 

Under ordinary conditions, however, the influx of sugar from the 
digestive tract is more or less intermittent. After a meal rich in 
easily digestible carbohydrates, an abundant supply of it is taken 
up by the intestinal capillaries, while on a diet poor in carbohydrates 
or in prolonged fasting, the supply sinks to a minimum. This is, of 
course, especially true of animals like man and the carnivora in 
which the process of digestion is comparatively rapid, but even in 
herbivorous animals, with their more complicated digestive appara- 
tus, the rate of resorption of dextrose, and still more its absolute 
amount, must be more or less fluctuating. Evidently there must be 
some regulative apparatus which holds back from the general circu- 
ation any excess of dextrose, on the one hand, and prevents its 
being excreted unused, and on the other, supplements any lack 
resulting from a deficiency of the food in carbohydrates. This 
regulation is accomplished by the liver. 

Functions of the Liver. 

The functions of the liver in this regard appear to be twofold : 
First, it manufactures dextrose and supplies it to the general circu- 
lation ; and second, it serves as a reservoir, or a place of deposit, for 
any excess of carbohydrates supplied by the digestive apparatus. 

The Liver as a Source of Dextrose. — The blood as it 
comes from the intestinal capillaries, bearing the digested carbo- 
hydrates and proteids, enters the liver through the portal vein and 
is distributed by means of the capillary blood-vessels into which this 
vein divides through all parts of that organ, reaching the general 



METABOLISM. 19 

circulation again through the hepatic vein. In its passage through 
the capillaries of the liver, the blood is subjected to the action of the 
cells of the liver (hepatic cells). Our knowledge of the exact nature 
of this action is still more or less conjectural, in spite of a vast 
amount of experimental investigation, but certain general facts are 
pretty clearly established. 

In the first place, the hepatic cells appear to serve as a source of 
dextrose when no carbohydrates are supplied in the food. If a 
carnivorous animal be given a diet as free as possible from carbo- 
hydrates, as, for instance, prepared lean meat, consisting substan- 
tially of proteids, its blood still contains a normal amount of dex- 
trose and the blood in the hepatic vein is found to be richer in 
dextrose than that of the portal vein, showing that this substance 
is being formed in the liver. Moreover, while the percentage of 
dextrose in the blood is small, the total amount thus manufactured 
is very considerable. Seegen * estimates it at about one per cent, 
of the weight of the body in twenty -four hours. This is regarded 
by many physiologists as an overestimate, the considerable differ- 
ences in sugar content between the portal and hepatic blood found 
by Seegen being regarded as in part the effect of the necessary 
operation. Indeed, it is questioned by some whether any actual 
difference in sugar content between the portal and hepatic blood 
under normal conditions has been satisfactorily established analyti- 
cally, but the indirect evidence at least seems strongly in its favor. 

In the second place, the same outflow of dextrose from the liver 
appears to take place when the animal consumes a mixed diet con- 
taining carbohydrates. In this case also, except shortly after a 
meal containing much carbohydrates, the blood of the hepatic vein 
shows an excess of dextrose over that of the portal vein. The 
amount of dextrose thus introduced into the circulation is sub- 
stantially the same as in the first case, and its percentage in the 
blood is not perceptibly altered. The source of this dextrose, how- 
ever, is not so simple a question, since it is possible that all or a 
considerable portion of it may be supplied directly or indirectly 
by the dextrose resorbed by the intestinal capillaries. 

Granting the continual production of sugar by the liver, sub- 

* Die Zuckerbildung im Thierkorper, p. 115. 



20 PRINCIPLES OF ANIMAL NUTRITION. 

stantially two suppositions are open: On the one hand, we may 
consider that the resorbed carbohydrates of the food, after being 
temporarily stored up in the liver, as described below, are given off 
again without radical change and that the sugar-forming power of 
the hepatic cells is limited to the transformation of the proteids and 
perhaps the fats of the food. Or, on the other hand, we may sup- 
pose that the nutrients brought to the liver by the portal blood 
enter into the constitution of the protoplasm of the hepatic cells, 
and that the vital activity of this protoplasm gives rise to the dex- 
trose found in the blood, to the glycogen found in the liver, and to 
other products of whose nature we are largely ignorant. The 
evidence at hand is doubtless insufficient for a final decision between 
these alternatives, but the latter hypothesis would seem more in 
accord with our general knowledge of cell activity. As relates to 
the carbohydrates, it is supported by the fact that while various 
sugars besides dextrose (laevulose, mannose, galactose, sorbinose, 
and, as Munch * has shown, certain artificial hexoses) may be con- 
verted into glycogen, the resulting glycogen is always the same and 
the product of its hydration is always dextrose. f In other words, 
the molecular structure of these sugars is altered in a manner sug- 
gesting an assimilation by the hepatic cells rather than anything 
resembling an enzyme action. The subject can be more intelli- 
gently considered, however, in the light of a discussion of the second 
function of the liver. 

The Liver as a Reservoir of Carbohydrates. — When the 
food is rich in carbohydrates, the supply of dextrose to the blood 
through the intestinal capillaries is more or less intermittent. As 
a means of regulating this intermittent supply, the hepatic cells 
have the power of arresting the dextrose brought to them by the 
portal vein and converting it into an insoluble carbohydrate called 
" glycogen " or " animal starch " which is stored up in the liver. On 
the other hand, when the supply of carbohydrate food is cut off, 
and especially if all food be withdrawn, the glycogen of the liver 
rapidly diminishes, being apparently reconverted into dextrose. 
This latter phenomenon may be readily observed in the liver of a 
freshly killed animal. If the fresh liver, after removal from the 

*Zeit. physiol Chem . 29, 493. 

f Compare N^umeister. Physiologische Chemie, p. 326 



METABOLISM. 2 1 

body, be washed out by water injected through the portal vein till 
all sugar is removed, and if then, after standing for a time, the wash- 
ing be renewed, the first portions of water that pass contain sugar. 
The same process may be repeated several times. 

What is known as the glycogenic function of the liver was dis- 
covered by Claude Bernard in 1853, and has been the subject of a 
bewildering amount of discussion and controversy, both as to the 
origin of glycogen, its final fate, and its relations to the production 
of dextrose by the liver. Certain facts, however, may be regarded 
as established with at least a high degree of probability : 

First — The liver produces glycogen from dextrose and other 
(not all) carbohydrates, as above described. 

Second — The liver seems also to form glycogen from proteids, 
since this substance is found in considerable quantity in the livers 
of animals fed exclusively on meat. 

Third — Glycogen largely disappears from the liver during fast- 
ing, and to a considerable degree also in the absence of carbo- 
hydrates from the food. 

Fourth — The liver produces dextrose at an approximately con- 
stant rate, largely independent of the food-supply or the variations 
in the store of glycogen. 

These facts seem to point unmistakably to the sugar-producing 
function of the liver as the primary factor in the whole matter. The 
general metabolism of the body requires a constant proportion of 
dextrose in the blood, and as this dextrose is consumed the liver 
furnishes a fresh supply. This supply it manufactures from the 
materials brought to it by the blood of the portal vein. When 
carbohydrates are lacking in this blood, it apparently has the power 
of breaking down the proteids and perhaps the fats, thus supplying 
the needful dextrose. Some authorities claim that the same process 
goes on when carbohydrates are present, and it seems not unlikely 
that this is true, but when the food-supply consists so largely of 
carbohydrates as it does in the case of our domestic herbivorous 
animals, the conclusion seems unavoidable that at least a consider- 
able part of the dextrose consumed in the body must be derived 
from these substances. As already suggested, a very plausible view 
of the matter is to regard the resorbed nutrients of the portal blood 
as serving to feed the protoplasm of the hepatic cells and to look 



22 PRINCIPLES OF ANIMAL NUTRITION. 

upon the dextrose as one of the products of the metabolism of 
those cells. 

Since, however, the demands of the organism for dextrose and 
the supply of it, or of the materials for its manufacture, in the food 
do not keep pace with each other, sometimes one and sometimes the 
other being in excess, the liver has a second function. When the 
food-supply, of whatever kind, is in excess, instead of continuing to 
produce dextrose the metabolism in the liver takes a slightly differ- 
ent form and produces the insoluble glycogen, or perhaps the dex- 
trose of the portal blood is simply converted into glycogen without 
entering into the structure of the hepatic Drotaplasm. When, on 
the other hand, the food-supply is deficient, the stored-up glyco- 
gen is converted into dextrose; whether by some sort of enzyme 
action or by again serving as food for the hepatic protoplasm is 
uncertain. 

Fate of the Dextrose of the Blood. 

The fact that the proportion of dextrose in the blood is approxi- 
mately constant, notwithstanding the continual supply which is 
received from the liver, shows that there must be a continual abstrac- 
tion of dextrose from the blood, which is as continually made good 
by the activity of the hepatic cells. In fact, the dextrose of the 
blood appears to play a very prominent part in the animal economy, 
and the function of the liver in preparing it from other ingredients 
of the food is a most important one. 

Consumption in the Muscles. — From the point where it leaves 
the liver, our knowledge of the metabolism of the dextrose of the 
blood is scanty, but a large proportion of it undoubtedly takes 
place in the muscles. It was early shown by Chauveau that 
the proportion of dextrose in the blood diminishes in its passage 
through the capillaries of the body, so that the arterial blood con- 
tains more of this substance than the venous. In conjunction with 
Kauf mann * he has subsequently shown more specifically that in its 
passage through the muscular capillaries and through those of the 
parotid gland the blood is impoverished in dextrose, and to a much 
greater extent in the active than in the quiescent muscle. Coin- 

*Comptes rend., 103, 974 and 1057; 104, 1126 and 1352. 



METABOLISM. 23 

cident with this disappearance of dextrose, there is an increase in 
the carbon dioxide of the blood and a decrease of its oxygen. 

The relations of the dextrose of the blood to the evolution of 
heat and work in the muscles and other tissues, so far as they are at 
present understood, will be considered in a subsequent chapter. 
For our present purpose it suffices to note the fact that it disappears 
in the capillaries with the ultimate production of carbon dioxide 
and water. That the dextrose is immediately oxidized to carbon 
dioxide and water, however, is extremely unlikely. It has been 
suggested that the lactic acid which is found in the muscle after 
muscular contraction is one of the intermediate products of the 
oxidation. Several considerations, however, seem to render it 
more probable that the dextrose first enters in some way into the 
constitution of the muscles, or in other words, that a synthetic or 
anabolic process precedes the katabolic one. 

Muscular Glycogen. — Another fact, of much interest in this 
connection, is that the muscles (and other tissues also), as well as 
the liver, contain glycogen. Moreover, the muscular glycogen 
diminishes or disappears during work and reappears again after 
rest. It would appear, then, that the muscular tissue shares with 
the liver the ability to form glycogen. As in the case of the former 
organ, the simplest supposition is that this glycogen is produced 
from the dextrose supplied in the blood, and Kiiltz * and others 
have shown that subcutaneous injections of sugar give rise to a 
formation of muscular glycogen in frogs whose livers have been 
removed. On the other hand, of course, the considerations pre- 
sented above relative to the sources of the liver glycogen apply, 
ceteris 'paribus, to the formation of glycogen in the muscles. Neither 
the source nor the exact functions of the muscular glycogen are 
yet beyond controversy, but the facts just stated strongly suggest 
a storing up of reserve carbohydrates during rest to be drawn upon 
when there is a sudden demand for rapid metabolism. 

Fat Production. — In addition to its important relation to the 
muscles, the dextrose of the blood likewise supplies nourishment 
for the fat tissues of the body. Hitherto we have spoken as if the 
supply of dextrose to the blood were determined substantially by 

* Neumeister, Physiologische Chemie, p. 322. 



24 PRINCIPLES OF ANIMAL NUTRITION. 

the demands of the general metabolism for material to produce heat 
and motion. Plainly, however, the capacity of the muscles and 
the liver to store up carbohydrates is limited, and if the food-supply 
is permanently greater than the demands of the organism, some 
other provision must be made for the excess. Under these circum- 
stances the superfluous dextrose which finds its way into the blood 
gives rise to a production of fat, which is stored up as a reserve in 
special tissues and apparently does not enter again into the general 
metabolism until a permanent deficiency in the food-supply occurs. 
The experimental evidence of the production of fat from carbo- 
hydrates, as well as the quantitative relations of the process so far as 
they are known, will be considered subsequently. In its relations 
to the economy of the organism the process is analogous to the 
formation of glycogen in the liver, except that the storage capacity 
of the fat tissues is vastly greater, but as compared with the forma- 
tion of glycogen it is distinctively an anabolic process, the fat 
molecule being more complex and containing more potential energy 
than that of dextrose. Hanriot,* assuming the formation of olein, 
stearin, and palmitin in molecular proportions, represents the 
process by the equation: 

13C 6 H 12 6 = C 55 H 104 O 6 + 23C0 2 + 26H 2 0. 

PENTOSE CARBOHYDRATES. 

The facts of the foregoing paragraphs relate primarily to the 
hexose carbohydrates, particularly starch and sugar, and to a con- 
siderable extent to the metabolism of carnivorous animals. The 
food of herbivora, however, contains a great variety of carbohy- 
drates and especially considerable quantities of the pentose or five- 
carbon carbohydrates. That these substances are in part digest- 
ible, or that at least a considerable proportion of them disappears 
from the food during its transit through the alimentary canal, was 
first shown by Stone, f and has since been fully confirmed by the 
investigations of Stone & Jones % and of Lindsey & Holland, S 
but of their further fate in the body relatively little is known. 

* Archives de Physiol., 1893, 248. % Agricultural Science, 5, 6. 

t Amer. Chem. Jour., 14, 9. §Ibid., 8, 172. 



METABOLISM. 25 

Ebstein,* who was the first to investigate this subject, showed 
qualitatively the presence of pentose carbohydrates in the urine of 
man after the ingestion of arabinose and xylose even in very small 
doses, and concluded that these sugars are not assimilable. 

Salkowski f shortly afterward observed the appearance of pen- 
toses in the urine of rabbits given arabinose after five or six days of 
fasting. He found in the urine, however, only about one-fifth of 
the amount ingested, together with small amounts in the blood and 
larger ones in the muscles, but there was a considerable increase of 
the glycogen of the liver. From the latter fact Salkowski con- 
cludes that arabinose may be, either directly or indirectly, a source 
of glycogen. The glycogen found in his experiment was the ordi- 
nary six-carbon glycogen. 

Subsequent investigations by Cremer, % Munk,§ FrentzelJ Linde- 
mann & May,!" Fr. Voit,** Jacksch,ff Miinch,tJ Salkowski,§§ 
and others have been directed largely to two questions, viz., 
whether the pentose carbohydrates are oxidized in the body and 
whether they serve as a source of glycogen. 

Pentoses Oxidized in the Body. — As the general result of 
these investigations, it may be stated that pentoses (in particular 
arabinose and xylose), whether administered by the stomach or 
injected into the blood, are at least partially oxidized in the body. 
In the human organism the power of oxidizing the pentoses, which 
do not normally constitute any considerable portion of its food, 
appears to be quite limited, and even when they are given in small 
quantities a portion (not all) is excreted in the urine. In the rabbit 
the pentoses seem to be more vigorously oxidized, only about 
twenty per cent, being excreted unaltered, even when compara- 
tively large doses are given. 

In these experiments the pentose sugars were administered in 
considerable amounts at once, and the excretion of a portion unal- 
tered would seem to be a phenomenon similar to the temporary 

*Virchow's Archiv, 129, 401; 132, 368. If Arch. klin. Med., 56, 283. 

fCentralbl. med. Wiss., 1893, p. 193. **Ibid., 58, 524. 

JZeit. f. Biol., 29, 536; 42, 428. ft Zeit. f. Heilk., 20, 195. 

gCentralbl. med. Wiss., 1894, p. 83. jj Zeit. physiol. Chem., 29, 493. 

|| Arch. ges. Physiol., 56, 273. %%Ibid., 82, 393. 



26 PRINCIPLES OF ANIMAL NUTRITION. 

glycosuria caused by large doses of the common sugars. The pen- 
tose carbohydrates in the ordinary food of herbivora, however, are 
largely or entirely the comparatively insoluble pentosans. As 
already stated, these bodies are partially digested — that is, they do 
not reappear in the feces. As to the manner of their digestion we 
are ignorant. If we are justified in assuming that the digested 
portion is converted, wholly or partially, into pentoses, then the 
conditions differ from those of the experiments above mentioned 
in that the production and assimilation of the pentoses is gradual. 
Under these circumstances we might be justified in anticipating 
a more complete oxidation of these bodies. To what extent this 
is true it is at present impossible to say. Weiske,* in connection 
with his investigations upon the digestibility of the pentosans, states 
that the urine of the sheep and rabbits experimented upon gave 
only a slight reaction for pentoses. The writer has not been able 
to find any records of other tests of the urine of domestic animals 
for pentoses. 

Pentoses as a Source of Glycogen. — Most, although not 
all, investigators have found an increase in the glycogen of the liver 
consequent upon the ingestion of pentoses, but in every case it has 
been the ordinary six-carbon glycogen. This has been commonly 
and most naturally interpreted as showing that the pentoses are not 
themselves converted into glycogen in the body, but are simply 
oxidized in the place of some other material which is the true source 
of the observed gain of glycogen. In the light of known facts 
regarding the apparent power of the liver to produce glycogen from 
very diverse hexoses (see p. 20) it would seem, however, that the 
possibility of an actual assimilation of the pentoses by the hepatic 
cells should at least be borne in mind. 

THE ORGANIC ACIDS. 

In addition to such quantities of the organic acids, free and com- 
bined, as are contained in their food, relatively large amounts of 
these substances are, in the case of herbivorous animals and par- 
ticularly of ruminants, produced by the fermentation of the carbo- 
hydrates in the alimentary canal. For this reason their meta- 

*Zeit. physiol. Chem., 20, 489. 



METABOLISM. 27 

bolism may properly be considered in connection with that of the 
carbohydrates themselves. 

But little is known of the metabolism of the organic acids, how- 
ever, beyond the fact that they are oxidized in the body, a portion 
of the resulting carbon dioxide appearing in the urine, in combina- 
tion with sodium and potassium, rendering that fluid alkaline. 
Wilsing * and v. Knieriem f have shown that organic acids such as 
result from the fermentation of carbohydrates are not found to any 
appreciable extent in the excreta, while the researches of Munk J 
and Mallevre,§ which will be considered more particularly in 
another connection, have shown that the sodium salts of butyric 
and acetic acids when injected into the blood are promptly oxi- 
dized, and Nencki & Sieber || have shown that lactic acid is 
readily oxidized, even by a diabetic patient. 

NON-NITROGENOUS MATTER OF THE URINE. 

It has been implied in the foregoing pages that the digested 
carbohydrates of the food, whatever the intermediate stages through 
which they may pass, are ultimately oxidized to carbon dioxide and 
water. Of the ordinary hexose carbohydrates this is doubtless 
true, but with some of the large variety of substances ordinarily 
grouped together, by the conventional scheme of feeding-stuffs analy- 
sis, as "carbohydrates and related bodies," or as "crude fiber" 
and "nitrogen-free extract," the case appears to be otherwise. 

It has been shown that the urine, in addition to the nitrogenous 
products of proteid metabolism which will be considered in a 
subsequent section, contains also non-nitrogenous materials, pre- 
sumably metabolic in their nature. In the urine of man and of the 
carnivora these non-nitrogenous substances are chiefly or wholly 
such as might be derived from the metabolism of proteids (phenols 
and other compounds of the aromatic series), and their amount is 
comparatively small. In the urine of herbivora, particularly of 
ruminants, however, their quantity is relatively very considerable, 
and it seems impossible to regard any large portion of them as 
derived from the proteid metabolism. 

*Zeit, f. Biol., 21, 625. J Arch. ges. Physiol., 46, 322. 

flbid., 21, 139. %Ibid., 49, 460. 

,|| Jour. pr. Chem., N. P.', 26, 32. 



28 PRINCIPLES OF ANIMAL NUTRITION. 

Henneberg * found that from 26.7 to 30.0 per cent, of the organic 
matter of sheep urine was neither urea nor hippuric acid, while from 
95 to 100 per cent, of the total nitrogen was contained in these two 
substances. G. Kiihn in his extensive respiration experiments on 
oxen, as reported by Kellner,f assuming that all the nitrogen of 
the urine was in the form either of hippuric acid or urea, found that 
from 40.05 to 67.64 per cent, of the total carbon of the urine was 
present in non-nitrogenous substances. The more recent investi- 
gations of Kellner,! as well as those of Jordan § and of the writer, || 
have fully confirmed this fact. 

Apparently these non-nitrogenous organic substances are de- 
rived in some way largely from the coarse fodders. Their propor- 
tion in the urine is relatively large when the ration consists exclu- 
sively of coarse fodder, and the addition of such fodders to a basal 
ration causes a marked increase in their amount, while, on the 
other hand, such concentrated feeding-stuffs as have been inves- 
tigated do not produce this effect in any very marked degree. 
Furthermore, their amount seems to bear no fixed relation to the 
protein of the coarse fodder. When the amount of the latter 
ingredient is small, the total organic matter of the urine has in 
some cases exceeded the maximum amount that could have been 
derived from the protein of the food, thus demonstrating that a 
portion at least of the non-nitrogenous urinary constituents must 
have had some other source. As the proportion of protein in the 
food increases, the amount of nitrogenous products in the urine 
likewise increases, while that of the non-nitrogenous products 
appears to be more constant, so that the ratio of urinary nitrogen 
to carbon increases. The most plausible explanation of these facts 
seems to be that the substances in question are derived from some of 
the non-nitrogenous ingredients of the coarse fodders, but from what 
ones, or what is the nature of the products, we are still ignorant.!" 

*Neue Beitrage, etc., p. 119. 
fLandw. Vers. Stat., 44, 348, 404, 474, 529. 
\Ibid., 47, 275; 50, 245; 53, 1. 
§New York State Expt. Station, Bull. 197, p. 27. 
|| Penna. Expt. Station, Bull. 42, p. 150. 

\ A further discussion of this subject in its relations to the energy of 
the food will be found in Part II. 



METABOLISM. 29 



§ 2. Fat Metabolism. 

Scarcely a tissue or portion of the animal body can be named 
in which more or less fat is not found. The muscular fibers, the 
epithelium, the nerves and ganglia, etc., all contain cells in which 
globules of fat may be recognized, so that the capacity to produce 
or store up fat seems to be common to almost all the cells of the 
body. It is particularly in certain cells of the connective tissue, 
however, that the large accumulations of visible fat in the body 
take place. At the outset these cells present no special characters, 
but in a well-nourished animal globules of fat begin to accumulate 
in them, the cells enlarge, the globules of fat coalesce into larger 
ones, and finally the cell substance is reduced to a mere envelope, 
the nucleus being pushed to one side and almost the whole volume 
of the cell occupied by fat. Masses of connective tissue thus loaded 
with fat constitute what is called adipose tissue. Large deposits 
of adipose tissue are met with surrounding various organs, particu- 
larly the kidneys, but the largest deposit of fat is usually in the 
connective tissue underlying the skin. In milk production, too, 
large amounts of fat appear in the epithelial cells of the milk glands. 

Fat Manufactured in the Body. — The older physiologists held 
that all the ingredients of the body pre-existed in the food. Specifi- 
cally, animal fat was regarded as simply vegetable fat which had 
escaped oxidation in the body and been deposited in the tissues. 
But while there is no doubt that the fat of the food can contribute 
to the fat supply of the body, the food of herbivorous animals 
usually contains a relatively small quantity of fat and the amount 
produced by a rapidly fattening animal or by a good dairy cow is 
usually much greater than that consumed in the food. 

Deferring to subsequent pages a discussion of the sources of 
animal fat,* we may content ourselves here with anticipating the 
general results of the great amount of experimental inquiry which 
has been expended upon this question. These results may be 
briefly summarized in the following statements : 

* For a very complete review of the literature of fat production up to 1894, 
see Soskin, Journ. f. Landw., 42, 157. K 



30 PRINCIPLES OF ANIMAL NUTRITION. 

1. The animal body produces fat from other ingredients of its 

food. 

2. The carbohydrates and related bodies of the food serve as 

sources of fat. 

3. It is probable that the proteids also serve as sources of fat. 

So far, then, as that portion of the fat which is actually pro- 
duced in the body from other substances is concerned, we may most 
readily conceive of its formation as consisting essentially of a 
manufacture of fat by the protoplasm of the fat cells, which are 
nourished by the carbohydrates, proteids, and other materials 
brought to them by the circulation. 

Functions of the Food Fat. — The fat which is manufactured 
in the body from other ingredients of the food, however, often con- 
stitutes the larger portion of the total fat production, while but 
a relatively small proportion at most can be derived from the fat 
of the food. The question naturally arises whether this smaller 
portion contained in the food is simply deposited mechanically, so 
to speak, in the fat cells, or whether it too, like the carbohydrates 
and proteids, serves to nourish the fat cells and supply raw material 
out of which they may manufacture fat. 

At first thought the former alternative might seem more prob- 
able. The fat of the food, so far as we are able to trace it, does not 
undergo any considerable chemical changes, such as the proteids 
do, e.g., in the process of digestion, but is largely resorbed in the 
form of apparently unaltered fat. Moreover, resorption of fat takes 
place largely through the lacteals and the resorbed fat reaches the 
general circulation without being subjected like the carbohydrates 
to the action of the liver. 

Deposition of Foreign Fats. — The view just indicated is 
supported to a considerable extent by the results of experiments 
upon the fate of foreign fats introduced into the body. 

Experiments by Radziejewsky * and Subbotin f were indecisive, 
but Lebedeff % was later successful in obtaining positive re- 
sults. Two dogs, after prolonged fasting, received small amounts 
of almost fat-free meat together with, in the one case, linseed oil, 

*Virchow's Archiv., 56, 211 ; 43. 268. fZeit. f. Biol.. 6, 73. 

JThier. Chem. Ber.. 12,425; Zeit. Physiol. Chem.. 6, 149; Centralbl. med. 
Wiss.. 1882.. 129. 



METABOLISM. 3 1 

and in the other, mutton tallow. After three weeks, during which 
the animals recovered their original weights, the adipose tissue was 
found to contain, in the one case, fat fluid at 0° C. and agreeing very 
closely with linseed oil in its chemical behavior, while in the other 
case the fat had a melting-point of over 50° C, and was almost 
identical with mutton fat. On the other hand, the same author 
in experiments with tributyrine failed to obtain any noteworthy 
deposition of this substance. 

Munk * fed large amounts of rape oil to a previously fasted dog 
for seventeen days and found in the body considerable amounts 
of fat differing markedly in appearance and properties and in the 
proportion of olein to solid fats from normal dog fat. He likewise 
succeeded in isolating from the fat eruic acid, the characteristic 
ingredient of rape oil. In a second experiment f the fatty acids 
prepared from mutton tallow were fed with similar results, the 
proportion of stearin and palmitin to olein being approximately 
reversed as compared with normal dog fat. The latter experiment 
is also of interest as showing that the fatty acids may be synthesized 
to fat in the body, the change taking place, according to Munk, in 
the process of resorption. 

More recently Winternitz J has experimented with the iodine 
addition products of fats. He observed the retention of a con- 
siderable proportion of iodine in the body (of hens and dogs) in 
organic form and also found iodine in the fat of the body at the close 
of the experiment. Similar experiments on a milking goat § showed 
that at least 6 per cent, of the fat fed passed into the milk. 

Henriques and Hansen 1 1 fed two three-months-old pigs for about 
nine months with ground barley, to which was added, in one case 
linseed oil and in the other cocoanut oil, while in the succeeding 
three months the rations were exchanged. Samples of the sub- 
cutaneous fat of the back were taken (with the aid of cocaine) at 
four different times and the fat of the carcasses at the close of the 
experiment was also examined. The results showed an abundant 
deposition of the linseed oil (and cocoanut oil?). On the other 

*Thier. Chem. Ber., 14, 411; Virchow's Archiv., 95, 407. 
f Archiv. f. (Anat. u.) Physiol, 1883, p. 273. 
% Zeit. physiol. Chem , 24, 425. 
§Thier. Chem. Ber., 27, 293. 
1 Ibid., 29. 68. 



32 PRINCIPLES OF ANIMAL NUTRITION. 

hand, experiments with cows failed to show any passage of linseed 
oil as such into the milk. 

Leube * made subcutaneous injections of melted butter on two 
dogs and found an abundant deposit of butter fat especially under 
the skin of the abdomen, the Beichert-Meissl number of the fat 
being 20.46 in the first case and 15.3 in the second. Rosenfelt f 
fed fasted dogs with mutton fat and observed a large deposit 
of this fat in all parts of the body. 

Influence of Feeding on Composition of Fat. — In addition 
to the more purely physiological experiments just cited, there are 
on record a not inconsiderable number of feeding experiments, 
especially upon swine, in which the feeding appears to have 
sensibly influenced the appearance, firmness, melting-point, or 
composition of the body fat. 

While it is not impossible, however, that in some cases the 
peculiar fats of the food (e.g., the fat of maize or of the oil-meals) 
may have been deposited in the adipose tissue unchanged, it must 
be borne in mind that these experiments were made on mixed rations 
and that undoubtedly there was a considerable production of fat in 
the body from other ingredients of the food. This being the case, 
we are left in doubt as to whether the effect observed is due directly 
to the fat of the food or is to be explained as an effect of the food as 
a whole, or of some unknown ingredients of it, in modifying the 
nature of the metabolism in the fat cells. That such an explana- 
tion is at least possible would seem to be indicated by the well- 
established fact that marked changes of food do modify the 
metabolism in the milk gland sufficiently to materially affect the 
proportion of volatile fatty acids in butter fat. 

A striking example of the possibility of such an effect upon the 
metabolism of the fat cells is afforded by the recent investigations of 
Shutt % into the causes of " soft " pork. On the average of a con- 
siderable number of animals, he finds that the shoulder and loin fat 
of pigs fed exclusively on maize shows a very low melting-point 
and a high iodine absorption number, indicating a large percentage 
of olein, and inclines to attribute this effect to the oil of the maize. 
When, however, he fed skim milk with the maize, he obtained pork 

* Thier. Chem. Ber., 25, 45. \ Ibid., 25, 44. 

\ Canada: Dominion Experiment Station, Bull. 38. 



METABOLISM. 33 

of good quality, the fat having a melting-point and iodine number 
not widely different from those obtained with the most approved 
rations. While it is possible that part of this effect was due to a 
reduced consumption of maize oil, so that more fat was produced 
from the other ingredients of the food, the conclusion seems justified 
that the principal factor was the influence of the skim milk upon 
the nutrition of the fat cells. This influence may with some degree 
of probability be ascribed to its protein, and it is worthy of notice 
that in Shutt's experiments the rations which produced the highest 
grade of pork were composed of materials rich in protein. 

Another fact warns us to be cautious in our interpretation of 
the results of this class of feeding experiments. Such experiments 
in most cases involve a comparison of the composition of the fat 
from animals differently fed. Albert * has found that both with 
swine and sheep the composition of the body fat is subject to very 
considerable individual variations as to melting-point, refractive 
index, and iodine number, the differences being, in his experiments, 
greater than the average differences which could be ascribed to the 
feeding. 

Moreover, the fat of the same individual has not the same com- 
position in different parts of the body. This point has recently 
been the subject of an elaborate investigation by Henriques & 
Hansen, f whose results show a higher melting-point and a lower 
iodine number in the inner as compared with the outer layers of 
fat. This difference they ascribe to the difference in the tempera- 
ture of the tissues and support this view by an experiment with 
three pigs. One animal was kept in a stall heated to about 30° C. 
for two months, while the others were exposed to a temperature of 
0° C, one unprotected and the other partially enveloped in a sheep- 
pelt. At the close of the experiment the fat immediately under 

the skin gave the following figures: 

Iodine Solidifying 

Number. Point. 

Kept at 30°-35° C. . .' 69.4 24.6° C. 

Kept at 0°, in sheep pelt: 

Part under the pelt 67.0 25.4° C. 

Part exposed 69.4 24.1° C. 

Kept at 0°, unprotected 72.3 23.3° C. 

* Landw. Jahrb., 28, 961, 986. 

t Bied. Centr. Blatt. Ag. Ch., 30, 182. 



34 



PRINCIPLES OF ANIMAL NUTRITION. 



Towards the interior of the body the differences became grad- 
ually less. 

It is evident; then, that the sources of possible error in ex- 
periments upon the influence of food on the composition of body 
fat are considerable, and that not only is great care necessary to 
secure representative samples of fat for examination, but the effect 
of individuality must be eliminated so far as possible by the use 
of a considerable number of animals. When we add to this the 
other fact that the fat production of herbivorous animals is 
largely at the expense of other nutrients than fat, we shall hardly 
incline to give the results of such investigations much weight as 
regards the question of the functions of food fat. 

Quantitative Relations. — Some further light upon the point 
under discussion may perhaps be obtained from a consideration of 
the quantitative relations of food fat to fat production shown by 
respiration experiments and which will be considered more fully 
on subsequent pages (compare Chapter V). In scarcely any of these 
experiments has the food fat been deposited quantitatively in 
the tissue. In three out of five experiments by Rubner in which 
fat was given to a previously fasting animal, from 65.82 to 91.89 
per cent.' of the fat supplied in excess of the amount metabolized 
during fasting was stored up in the body. Similarly, in the ex- 
periments of Pettenkofer & Voit, in which the fat was added to a 
ration already more than sufficient for maintenance, on the average 
87.86 per cent, of the fat of the food was deposited in the tissues. 

Kellner,* among his extensive respiration experiments upon 
cattle, reports the results of three in which peanut oil was added to a 
basal ration more than sufficient for maintenance. The amounts 
of fat consumed in excess of the basal ration and the resulting gains 
by the animals were as follows, the slight variations in the amounts 
of the other nutrients being neglected: 





Additional Fat 

Digested, 

Grams. 


Gain by Animal. 


Gain of Fat 


Animal. 


Protein, 
Grams. 


Fat, 
Grams. 


in Per Cent, of Fat 
Digested. 


D 

F 
G 


677 
542 
458 


8 
86 
44 


239 
205 
279 


35.30 
37.83 
60.91 



* Landw. Vers. Stat., 53. 112, 124. 199. 214. 



METABOLISM. 35 

Computations of the proportion of the energy of the added fat 
which was recovered in the total gain of flesh and fat (compare 
Chapter XIII, § 1) showed, according to the method of computa- 
tion employed, a loss of from 31 to 48 per cent. 

The comparatively small losses observed in Rubner's and in 
Pettenkofer & Voit's experiments may well be ascribed to a con- 
sumption of energy in the work of digestion (compare Chapter 
XI), but it hardly seems possible to account in this way for 
the large losses observed by Kellner. Apparently the peanut 
oil in these experiments, after its digestion and resorption, must 
have been subjected to extensive molecular changes involving a 
considerable expenditure of potential energy, and if this be true, 
the suggestion of an assimilation by the fat cells and a construction 
of animal fat from the oil is obvious. 

Constancy of Composition of Fats. — The relatively constant 
and characteristic composition of the fat of the same species of 
animal, notwithstanding differences in the food, has been urged in 
favor of the view that the fat of the animal is a product of the 
protoplasmic activity of the fat cells. "The fat of a man differs 
from the fat of a dog, even if both feed on the same food, fatty or 
otherwise" (M. Foster). The steer produces beef fat and the sheep 
mutton fat on identical rations. Unless, however, we are prepared 
to discredit the experimental results above cited, it would appear 
that this general and approximate uniformity of composition is 
largely due to a general uniformity of food, and that marked changes 
in the nature of the latter may result in altering the former. To this 
must be added, as already insisted upon, the fact that much of the 
fat found in the body, especially in the herbivora, is undoubtedly 
produced in the organism. We may fairly presume that this fat 
will be the characteristic fat of the species. If we may suppose 
further that a considerable share of the food fat is oxidized directly, 
and if we take into consideration the general uniformity of diet of 
our domestic animals and the relatively small total amount of fat 
which it often contains, we have at least a plausible explanation of 
the observed facts and one which does not preclude a direct deposi- 
tion of food fat in the body and a consequent effect upon the com- 
position of the body fat. 

The Katabolism of Fat. — The proportion of the food fat which 



3 6 PRINCIPLES OF ANIMAL NUTRITION. 

serves to increase the store of fat in the body depends largely upon 
the total food-supply. When the latter is more than sufficient to 
balance the total metabolism of the organism, the excess may give 
rise to a storage of fat, and under these circumstances the food fat 
or a part of it may, as we have seen, contribute to the increase 
of adipose tissue. On the other hand, when the food-supply is in- 
sufficient, not only is its fat in common with its other ingredients 
in effect consumed to support the vital processes, but the fat pre- 
viously stored in the adipose tissue is drawn upon to make up the 
deficiency. Under these circumstances the fat disappears more or 
less rapidly from the fat cells, passing away gradually either into 
the lymphatics or the blood-vessels in some manner not as yet fully 
understood. 

Fat, then, whether derived immediately from the food or drawn 
in the first instance from the adipose tissue of the body, passes into 
the circulation and serves to supply the demands of the body 
for oxidizable material and energy, the final products of its oxida- 
tion being carbon dioxide and water. Of the intermediate steps 
in this katabolic process we are comparatively ignorant, but one 
hypothesis regarding it has acquired so much importance in its 
bearings on the availability of the potential energy of the food as to 
require mention here. 

Formation of Dextrose from Fat. — This hypothesis is, in 
brief, that the first step in the katabolism of fat takes place in the 
liver and consists in its conversion into sugar. In other words, it is 
held that the fat of the food or that drawn from the adipose tissue 
of the body supplies the liver with part of the material for its func- 
tion of sugar production described in the previous section. 

This hypothesis is advocated especially by those physiologists 
who, like Seegen in Vienna and Chauveau and his associates in Paris, 
look upon the carbohydrates, and particularly dextrose, as the im- 
mediate source of the energy exerted in muscular contraction or 
in the various other forms of physiological work. The evidence 
upon which this view is based will be considered in subsequent 
chapters. For the present it suffices to point out that, if we admit 
its truth, then the general metabolism of the body is essentially a 
carbohydrate metabolism. Whether we consider the case of a 
fasting animal, living upon its store of protein and fat, or that of an 



METABOLISM. 37 

animal receiving food, the liver breaks down the proteids and fat 
supplied to the blood either by the food or from the tissues, pro- 
ducing dextrose. This dextrose, like that derived from the carbo- 
hydrates of the food, is then, as indicated in the previous section, 
oxidized in the tissues either directly or with previous conversion 
into glycogen. 

As regards the katabolism of fat, in particular, Nasse * has 
brought forward reasons for believing that the liver is concerned in 
it. Seegen f submitted fat to the action of finely chopped, freshly 
excised liver suspended in defibrinated blood at a temperature of 
35-40° C, in a current of air and observed a considerable formation 
of sugar in five to six hours as compared with a control experiment 
without the fat. He likewise found \ in experiments upon dogs 
fed on fat with little or no meat that the blood of the hepatic vein 
was much richer in sugar than that of the portal vein. On the basis 
of the probable amount of blood circulating through the liver, he 
computes that the total amount of sugar thus produced was much 
greater than could have been supplied by the glycogen stored in 
the liver and the amount of proteids metabolized (as measured 
by the urinary nitrogen), and hence concludes that at least the 
difference was produced from fat. As was pointed out in the 
preceding section, however, many physiologists regard the large 
differences between the dextrose content of the portal and the 
hepatic blood observed by Seegen as being in large part the result of 
the necessary operation and thus abnormal, and the production of 
glycogen or dextrose from fat is not regarded as proven by the 
majority of physiologists. § Thus Girard || and Panormow 1" found 
the post-mortem formation of sugar in the liver to be strictly pro- 
portional to the disappearance of glycogen, and similar results 
were obtained by Cavazzani and Butte.** 

Kaufmann,ft "who has developed this hypothesis in considerable 

* v. Noorden, Pathologie des Stoffwechsels, p. 85. 

| Die Zuckerbildung im Thierkorper, p. 151. 

% Ibid., p. 171. 

§ Cf. Neumeister, Physiologische Chemie, p. 368. 

II Arch. ges. Physiol., 41, 294. 

1 Thier. Chem. Ber., 17. 304. 

** Ibid., 24, 391 and 394. 

ff Archives de Physiol., 1896, p. 331. 



3& PRINCIPLES OF. ANIMAL NUTRITION. 

detail, represents the two supposed stages in the katabolism of fat 
by the two following equations, proposed by Chauveau:* 

First Stage : 2(C 57 H U0 O 6 ) + 670 2 = 16(C 6 H 12 6 ) + 18C0 2 + 14H 2 0. 

Second Stage: 16(C 6 H 12 6 ) +960 2 = 96C0 2 + 96H 2 0. 

Even, however, if we admit the formation of dextrose from fat 
in the body, it may fairly be doubted whether the process is as 
simple as these equations, even if regarded as simply schematic, 
would imply. 

§ 3. Proteid Metabolism. 

ANABOLISM. 

Digestive Cleavage. — The digestion of the proteids is essen- 
tially a process of cleavage and hydration under the influence of 
certain enzyms. By this process the complex proteid molecules 
are partially broken up into simpler ones. By the action of pepsin 
in acid solution we obtain albumoses and peptones, while the 
trypsin of the pancreatic juice, at least outside the body, carries 
the cleavage still further, producing crystalline nitrogenous bodies of 
comparatively simple constitution. Opinions are still more or less 
divided as to how far these processes of cleavage and hydration are 
carried in the actual process of digestion, where the products of the 
action are constantly being resorbed, but there are not wanting in- 
dications that it is both less extensive and less rapid than in arti- 
ficial digestion. It likewise seems to have been demonstrated that 
some soluble proteids are capable of direct resorption without 
change, while others are not and some, notably casein, are promptly 
coagulated by the rennet ferment, apparently expressly in order 
that they may be subjected to the action of the digestive ferments. 
In a general way, the statement appears to be justified that the 
larger share of the proteid material of the food is resorbed as 
albumoses and peptones. 

Purpose of the Cleavage. — The fact just mentioned that, 
on the one hand, some soluble proteids appear capable of direct re- 
sorption, while, on the other hand, some, like casein, are at once 
rendered insoluble as the first step in digestion, plainly necessitates 
a material modification of the old view that the object of the cleav- 
* La Vie et l'Energie chez l'Animale. 



METABOLISM. 39 

age and hydration of the proteids in digestion is to render them 
soluble. Undoubtedly this is an important function of the digestive 
fluids, but the fundamental object lies deeper and is found in the 
constitution of the proteids themselves. 

Nature of the Proteids. — While we are still very far removed 
from any adequate knowledge of the molecular structure of the 
proteids, a study of the action upon them of various hydrolytic 
agents, and particularly of the proteolytic enzyms of the digestive 
fluids, has shown that they undergo cleavage along certain definite 
lines, giving rise to two series of products known as the hemi- and 
the anti-series. The primary products are" the proteoses, or albu- 
moses (hemi and anti). By further action of the ferment these 
give rise to the secondary or deutero-proteoses, and these in turn 
to peptones, while the peptones of the hemi-series, by the further 
action of trypsin, are broken up, as noted, into simpler bodies such 
as aspartic acid, glutaminic acid, and notably tyrosin and leucin. 
The two latter bodies belong to the aromatic series and contain the 
phenyl radicle, which is thus shown to be present in the bodies of 
the hemi group, while it is absent from the anti group. Without 
pursuing the subject further, enough has been said to show that 
the general result of the digestive proteolysis is to break up the pro- 
teid molecule into a considerable number of unlike fragments.* 

Differences in Proteids. — Turning now to another phase of the 
subject, it is a familiar fact that the numerous proteids which have 
been studied differ quite markedly from each other in properties 
and in composition. To instance but a single characteristic differ- 
ence, the investigations of Osborne and his associates at the Connec- 
ticut Agricultural Experiment Station have shown in detail what 
was to a certain extent known before, viz., that the nitrogen con- 
tent of the vegetable proteids is notably higher than that of the 
animal proteids. We can only interpret these differences in com- 
position and properties as the results of differences in molecular 
structure. We may fairly suppose that these differences in struc- 
ture are brought about, in part at least, by differences in the relative 
proportions in the proteid molecule of the several molecular group- 
ings whose presence is indicated to us by the results of proteolysis. 

* For a full treatment of the subject, compare Chittenden, Digestive Pro- 
teolysis, 1894. 



40 PRINCIPLES OF ANIMAL NUTRITION. 

Food Proteids and Body Proteids. — What is especially to be 
noted in this connection is that the food proteids are not identical 
with the body proteids. This is especially true of the vegetable 
proteids in the food of the herbivora, and of the casein of milk, but is 
measurably true in all cases. A simple resorption of unaltered 
protein, therefore, would not serve the purposes of the organism. 
The food proteids must be changed to body proteids. This means, 
however, that the proportions of those molecular groupings which 
have just been spoken of must be changed — that is, the molecules 
of the food proteid must be so far broken down into their constituent 
molecular groupings as to permit of a rearrangement and repropor- 
tioning of the latter into molecules of body proteid. 

Such a partial breaking down of proteid material takes place in 
digestion, and indeed, as has been indicated above, it is the study of 
digestive proteolysis which has given us our general conception of 
the structure of the proteid molecule. The products of proteid 
digestion, then, as they are presented to the resorbent organs of the 
digestive tract, are no longer proteids, but the constituent molecular 
groupings out of which body proteids may be built up. 

Rebuilding of Proteids. — But while the proteids of the food are 
resorbed in the form of cleavage products, apparently largely as pep- 
tones, no trace of these bodies is found in the blood or in the lymph, 
nor even in the walls of the digestive canal. Still further, peptones 
when injected into the blood are treated by the organism as foreign 
substances and excreted as rapidly as possible, while if added in any 
considerable amount they act as poisons. The reconstruction of 
the proteid molecule from the fragments produced by the digestive 
process has been thought to take place in the epithelial cells of the 
intestines, the first product being probably serum albumen, so that 
we may say that the first step in proteid metabolism is anabolic. 

Recently, however, Okunew, working in Danilewsky's labora- 
tory, has announced the discovery that the enzym of rennet (chy- 
mosin) has the power of synthesizing peptones to proteids, and 
Saw j alow * has published further studies on the same subject. 
The latter investigator finds the product to be a gelatinizing pro- 
teid which is identical whatever the original source of the peptones 
and which he calls plastein. He considers that this plastein is 

♦Arch. ges. Physiol., 85, 171. 



METABOLISM. 41 

formed in the digestive canal and is the form in which the proteids 
of the food are resorbed, and points out that this hypothesis accounts 
for the hitherto puzzling fact of the occurrence of the milk-curdling 
ferment in animals, such as birds, fishes, and amphibia, which never 
consume milk. In further support of this view, Winogradow * 
finds the formation of chymosin in the stomach to be most active 
at the height of the digestive process, when peptones are being 
formed most freely. 

The proteid or proteids first formed from the albumoses and 
peptones, whether in the epithelial cells or by the action of 
chymosin, is subject to still further changes in other portions of the 
body, inasmuch as all the various nitrogenous tissues of the body 
are formed from it. Some of these changes may be slight, but 
others, as, e.g., the formation of the collagens, must be profound, 
while the formation of the compound proteids like haemoglobin, 
mucin, the nucleins, etc., is clearly synthetic and anabolic. As 
to where and how these changes and syntheses take place, we are 
largely ignorant. We simply know the general fact that the food 
proteids are first partially broken down in the process of digestion 
and then that the fragments are built up again into body proteids; 
first, probably, into some single form and later into still more com- 
plex bodies in the various tissues. 

KATABOLISM. 

Final Products. — The anabolic processes which have just been 
indicated might be characterized in general terms as a preparation 
of the food proteids for their diverse functions in the body. In the 
performance of those functions they, like all the organic ingredients 
of the body, undergo katabolic changes, liberating the energy which 
was originally contained in them or which may have been tem- 
porarily added in the preliminary anabolic changes. We have 
every reason to believe that the katabolism of proteids is a gradual 
process, passing through many intermediate stages, but we have 
very little actual knowledge of the steps which intervene between 
the proteids and bodies which are either excretory products 
themselves or closely related to them. Such information as has 

*Arch. ges. Physiol., 87, 170. 



42 PRINCIPLES OF ANIMAL NUTRITION. 

thus far been acquired upon this subject has resulted chiefly from 
attempts to trace back the excretory products to their antecedents. 

The products of the complete breaking down and oxidation of 
proteids in the body are carbon dioxide and water, excreted through 
the lungs, skin, and kidneys, and urea and a number of other com- 
paratively simple crystalline nitrogenous compounds found in the 
urine. To these are to be added the nitrogenous metabolic prod- 
ucts of the feces, the sulphuric and phosphoric acids resulting from 
the oxidation of the sulphur of the proteids and the phosphorus of 
the nucleo-proteids, and the relatively minute amounts of nitroge- 
nous matter found in the perspiration. 

Excretion of Free Nitrogen. — The question whether any 
portion of the nitrogen of the proteids is excreted as free gaseous 
nitrogen is one which has been the subject of no little investigation 
and controversy in the past, the especial champions being, on the 
affirmative, Seegen in Vienna and, on the negative, Voit in Munich. 
It would lead us too far aside from our present purpose, however, to 
attempt even to outline the evidence, and it must suffice to say that 
the great majority of physiologists regard it as established that there 
is no excretion of gaseous nitrogen as a result of the katabolism of 
proteids, but that all the proteid nitrogen is excreted in the urine 
and feces with the exception of small amounts in the perspiration. 
In accordance with this view, we shall assume in subsequent pages 
that the urinary nitrogen (together with, strictly speaking, the 
metabolic nitrogen of the feces and perspiration) furnishes a meas- 
ure of the total proteid katabolism of the body. 

A brief consideration of some of the principal nitrogenous 
products of proteid katabolism will serve to indicate some of the 
main features of the process, so far as they have been made out. 

Urea. — Urea, or dicarbamid, CON 2 H 4 , is the chief nitrogenous 
product of proteid metabolism in the carnivora and omnivora. In 
the urine of man, e.g., from 82 to 86 per cent, of the nitrogen is in 
the form of urea.* 

Antecedents of Urea. — A vast amount of study has been expended 
upon this question without as yet leading to any general unanimity 
of views. It appears, however, to be fairly well made out that at 

* v. Noorden, Pathologie des Stoffwechsels, p. 45. 



METABOLISM. 43 

least a considerable part if not all of the urea is formed in the liver, 
and that its immediate antecedent is ammonium carbonate, to 
which it is closely related chemically. This theory of Schmiede- 
berg's is supported by the facts: 

1st. That ammonium salts, and also the amid radicle NH 2 in 
the amido acids of the fatty series, when administered in the food 
are converted into urea. 

2d. That ammonium carbonate or formiate injected into the 
portal vein is converted in the liver into urea which appears in the 
blood of the hepatic vein. 

3d. That the administration of inorganic acids to the dog and to 
man results in the excretion of ammonium salts in the urine, it 
being supposed that the acid displaces the weaker carbonic acid 
and that the resulting ammonium salt is incapable of conversion 
into urea in the liver. 

4th. Severe disease of the liver has been observed to result in 
a decreased production of urea and an excretion of ammonium salts 
in the urine. 

Later investigations by Minkowski * and others have followed 
the process of the formation of urea one step further back and ren- 
dered it highly probable that the ammonium salts out of which urea 
is formed reach the liver in the form of ammonium lactate. It has 
been shown that sarcolactic acid is one of the products of the meta- 
bolism of the muscles. It would appear that this acid unites with 
the ammonium radicle derived from the proteids to form ammonium 
lactate, and that the latter on reaching the liver is first oxidized to 
the carbonate, which is then converted into urea. If, by disease 
or surgical interference, this action of the liver is prevented, ammo- 
nium lactate appears in the urine, and the same effect may even be 
produced by excessive stimulation of the proteid metabolism, so 
that the production of ammonium lactate exceeds the capacity of 
the liver to convert it. 

Uric Acid. — Uric acid is contained in small amounts in the 
urine of mammals. With birds it constitutes the chief nitrogenous 
product of the proteid metabolism. Of its antecedents in the 
organism scarcely anything is known. One theory regards it as a 
specific product of the metabolism of the nucleins, but this cannot 

*Cf. Neumeister, Physiologische Chemie, pp. 313-318. 



44 PRINCIPLES OF ANIMAL NUTRITION. 

be regarded as established, and appears difficult to reconcile with its 
relation to the proteid metabolism of birds. Others regard it as an 
intermediate product in the production of urea, a small portion of 
which escapes further oxidation by being excreted by the kidneys. 

Hippuric Acid. — This substance is a normal ingredient of the 
urine of mammals, but in that of man and the carnivora is found in 
but very small amounts. In the urine of herbivora, on the other 
hand, it occurs abundantly. 

Light was thrown upon its origin by the well-known discovery 
by Wohler, in 1824, that it is also found in large amount in the urine 
of man or of carnivora after the administration of benzoic acid. 
Chemically, hippuric acid is benzamido-acetic acid, or benzoyl 
glycocol. When the food contains benzoic acid the latter unites 
with glycocol resulting from the metabolism of the proteids and 
forms hippuric acid, while otherwise the glycocol would be further 
oxidized to simpler nitrogenous products. The synthesis of hip- 
puric acid has been shown to occur only in the kidneys in the dog, 
but in the case of the rabbit and frog they appear to share this 
capacity with other organs. 

In this action of benzoic acid we have the most familiar demon- 
stration of the formation of metabolic products intermediate be- 
tween the proteids and the comparatively simple nitrogenous sub- 
stances found in the urine. Glycocol has never been detected in the 
body, obviously because as fast as it is formed it is again decom- 
posed. Benzoic acid reveals its presence by seizing upon it and 
converting it into a compound which is incapable of further oxida- 
tion, and is therefore excreted. Other less familiar examples of 
the same fact might be cited did space permit. 

The normal presence of small quantities of hippuric acid in the 
urine, even when no benzoic acid is contained in the food, arises 
from the fact that the putrefaction of the proteids in the intestines 
yields aromatic compounds, containing the benzoyl radicle, which 
are resorbed and combine with glycocol to form hippuric acid. 
The origin of the large quantities of hippuric acid ordinarily ex- 
creted by herbivora, however, or rather of its benzoyl radicle, 
is still more or less of a puzzle, notwithstanding the consider- 
able amount of investigation which has been devoted to its 
study. The most natural supposition would be that the food of 



METABOLISM. 45 

these animals contains substances of the aromatic series capable 
of yielding benzoic acid or its equivalent in the body, but in none 
of the feeding-stuffs known to be efficient in causing an excretion 
of hippuric acid have such compounds been discovered in quantity 
even remotely sufficient to account for the hippuric acid produced. 

On the other hand, the hypothesis that the benzoyl radicle of 
the hippuric acid is derived to any large extent from the proteids 
of the food appears to be decisively negatived by several facts: 
First, the quantity of proteids in the ordinary rations of herbivora 
is relatively small, and even if it all underwent putrefaction the 
amount of aromatic products which could be formed, on any reason- 
able estimate, would account for only a small fraction of the hip- 
puric acid actually found.* Second, in several instances it has 
been observed that variations in the extent of the putrefactive 
processes in the intestines, as measured by the amount of con- 
jugated sulphuric acid in the urine (compare p. 46), bore no rela- 
tion to the variations in the production of hippuric acid. Third, 
the addition of pure proteids or of foods very rich in proteids to a 
ration does not increase the production of hippuric acid, and in at 
least one case f was found to diminish it and even stop it alto- 
gether. 

Apparently we must regard the non-nitrogenous ingredients of 
feeding-stuffs as the chief source of hippuric acid formation, but be- 
yond this our knowledge is rather vague. It is well established 
that the coarse fodders are the chief producers of hippuric acid, 
while the concentrated feeding-stuffs give rise to little or none, and 
may even reduce the amount previously produced on coarse fodder, 
as may also starch. Among the coarse fodders, the gramineae give 
rise to a markedly greater production of hippuric acid than the 
leguminosae. This effect of the coarse fodders naturally led to the 
suspicion that the crude fiber contained in them in large amounts 
might be the source of the hippuric acid, and in fact numerous 
experiments seem to show that some relation exists between the 
two, although the results of various investigators are far from con- 
cordant. 

Finally, the investigations of Goetze & Pfeiffer, \ and of 

* Compare Salkowski, Zeit. physiol. Chem., 9, 234. 
f Henneberg and Pfeiffer, Jour. f. Landw., 38, 239. 
JLandw. Vers. Stat., 47, 59. 



46 PRINCIPLES OF ANIMAL NUTRITION. 

Pfeiffer & Eber,* have shown with a high degree of probability 
that the pentose carbohydrates of the feed have some connection 
with the production of hippuric acid. The former investigators 
observed a marked increase in the production of hippuric acid by 
a sheep after the administration of cherry gum (impure araban) and 
of arabinose, and the latter obtained the same effect, although in a 
less marked degree, by feeding cherry gum to a horse. They also 
call attention to the differences in the behavior of the pentose carbo- 
hydrates in the organism of the herbivora and in that of man and 
the carnivora, but do not attempt to give a final solution of the 
problem of the origin of the hippuric acid in the former case, while 
they freely admit that it is difficult, if not impossible, to explain 
some of the facts already on record on the hypothesis that the pen- 
toses are the chief source of hippuric acid. 

Creatin and Creatinin. — Among other nitrogenous constit- 
uents of the urine of man and the carnivora may be mentioned 
creatinin. This body is the anhydride of creatin, and the two 
together constitute the principal part of the so-called flesh bases 
which are contained in considerable quantity in muscular tissue. 
When meat is consumed, its creatin is converted into creatinin and 
excreted quantitatively in the urine, the creatinin content of which 
may be thus considerably increased. As to the physiological signifi- 
cance of the creatin of muscular tissue opinions are divided, but 
good authorities are inclined to regard it as an intermediate 
product of the metabolism of the proteids which is ultimately con- 
verted into urea, and to urge that the fate of creatin taken into the 
stomach is not necessarily the same as that of the creatin produced 
in the muscles. 

Aromatic Compounds. — Besides the benzol radicle of hippuric 
acid, small amounts of other aromatic compounds are also found in 
the urine. These bodies, belonging chiefly to the phenol and indol 
groups, owe their origin exclusively to the putrefactive processes 
already mentioned as taking place in the intestines, and are found in 
the urine almost entirely in combination with sulphuric acid as the 
so-called conjugated sulphuric acids, so that the amount of the 
latter is employed as a measure of the extent of these putrefactive 
processes. 

*Landw. Vers. Stat., 49. 97. 



METABOLISM. 47 

Metabolic Products in Feces. — As already stated in Chapter 
I, the feces contain, in addition to undigested residues of the food, 
certain materials derived from the body of the animal. This fact 
was early recognized as true of both carnivora* and herbivora.f 
Of more recent investigations may be noted especially those of 
Miiller, J Rieder,§ and Tsuboi || on carnivora, those of Prausnitzl" and 
his associates on man, and those of Kellner,** Stutzer,f f Pfeiffer, \X 
and Jordan §§ on herbivora. 

These "metabolic products" appear to consist of unresorbed 
or altered residues of the digestive fluids and of mucus and other 
materials excreted or otherwise thrown off by the walls of the intes- 
tines. Their production goes on even when the digestive tract is 
void of food, producing the so-called fasting feces which constitute 
a true excretory product. The consumption of highly digestible 
food — e.g., lean meat — does not seem to materially increase their 
amount, but when food containing indigestible matter is eaten it is 
believed that they increase in quantity. 

It is presumed that these substances are largely nitrogenous in 
character, and it is known at any rate that not inconsiderable 
amounts of nitrogen may leave the body by this channel. In other 
words, these nitrogenous substances, derived from the proteids 
of the body, instead of undergoing complete conversion into the 
ordinary crystalline products have their katabolism interrupted 
as it were at an intermediate stage. 

Many attempts have been made to determine the amount of 
these metabolic products, or of their nitrogen, in the feces, but 
without much success, and it may fairly be said that at present 
we have no method which can be depended upon to distinguish 
sharply between the nitrogen of undigested-food residues and that 
of metabolic products. 

* Bischoff and Voit, Die Ernahrung des Fleischfressers, p. 291. 

fHenneberg, Beitrage, etc., 1864, p. 7. 

tZeit. f. Biol., 20, 327. 

% Ibid., 20, 378. 

\\Ibid., 35, 68. 

If Ibid., 35, 287; 39, 277; 42, 377. 

**Landw. Vers. Stat., 24, 434; Bied. Centralbl., 9, 763. 

ffZeit. physiol. Chem., 9,211. 

j|Jour. f. Landw., 31, 221; 33, 149; Zeit. physiol. Chem., 10, 561. 

§§ Maine Expt. Station Rep., 1888, p. 196. 



48 PRINCIPLES OF ANIMAL NUTRITION. 

Nitrogen in Perspiration. — The perspiration of such animals 
as secrete this fluid must be regarded as one of the minor channels by 
which nitrogen is excreted. In human perspiration there have been 
found, in addition to small amounts of proteids, urea, uric acid, 
creatinin, and other nitrogenous products of the proteid meta- 
bolism. In a recent investigation, Camerer * found about 34 per 
cent, of the total nitrogen of human perspiration to be in the form 
of urea, about 7.5 per cent, existed as ammonium salts, and the 
remainder in undetermined forms, including uric acid and traces 
of albumen. 

The total quantity of nitrogen excreted in the insensible perspi- 
ration appears to be insignificant. Atwater & Benedict f found 
it to amount to 0.048 gram per day for an adult man in a state 
of rest. Rubner & Heubner J obtained from the clothing of an 
infant 2.83 mgrs. of ammonia and 0.0205 mgr. of urea per day 
and estimated the total nitrogen of the perspiration at 39 mgrs. 

When the secretion of sweat is stimulated by work or a high 
external temperature the amount of nitrogen excreted may be con- 
siderably increased as compared with a state of rest, although its 
absolute amount is still small. Atwater & Benedict^ in a work ex- 
periment, observed an excretion of 0.220 gram of nitrogen per day 
in the perspiration of man. 

The Non-nitrogenous Residue of the Proteids. — The various 
nitrogenous products found in the urine and other excreta, the most 
important of which have been noticed above, are believed to con- 
tain all the nitrogen of the metabolized proteids. This does not 
imply, however, that a quantity of proteids equivalent to this nitro- 
gen, or even to that of the urine, has been completely oxidized to the 
final products of metabolism, viz., carbon dioxide, water, and urea 
and its congeners. 

A comparison of the ultimate composition of the proteids with 
that of the nitrogenous products of their metabolism reveals the 
fact that an amount of the latter sufficient to account for all the 
nitrogen of the proteids contain but a relatively small part of their 
carbon, hydrogen, and oxygen. Taking urea as the chief and 

*Zeit. f. Biol., 41, 271. 

fU. S. Dept. Agr., Office of Expt. Stations, Bull. 69, 73. 

tZeit. f. Biol., 36,34. 

§Loc. cit., p. 53. 



METABOLISM. 49 

typical metabolic product, and using average figures for the com- 
position of animal proteids, we have, omitting the sulphur of the 
proteids, the following: 

Proteids. Urea. Residue. 

Carbon 53.0 6.86 46.14 

Hydrogen 7.0 2.29 4.71 

Oxygen 24.0 9.14 14.86 

Nitrogen 16.0 16.00 

100.0 34.29 65.71 

After abstracting the elements of urea, we have left considerably 
over half the hydrogen and oxygen of the proteid and the larger 
part of its carbon. A substantially similar result is reached in case 
of the other nitrogenous metabolic products. The splitting off of 
these products from the proteids leaves a non-nitrogenous residue. 

Fate of the Non-nitrogenous Residue. — The foregoing 
statements and comparison must not be understood to mean that 
the proteids split up in the body into two parts, viz., urea, etc., on 
the one hand, and an unknown non-nitrogenous substance or sub- 
stances on the other. As we have already seen, the processes of 
proteid metabolism are far more complicated than such a simple 
cleavage. Neither are we to assume that any substance or group 
of substances corresponding in composition to the " residue " of the 
above computation exists. The figures mean simply that while 
the nitrogenous bodies of the urine contain all the nitrogen of the 
proteids they do not account for all of the other elements, but that 
part of the latter must be sought elsewhere. 

Ultimately, of course, the elements of this non-nitrogenous 
residue are converted into carbon dioxide and water. The conver- 
sion into these final products, however, is necessarily a process of 
oxidation, presumably yielding energy to the organism. It is a 
matter of some interest, then, to trace the steps of the transforma- 
tion bo far as this is at present possible. 

Formation of Sugar. — In discussing the functions of the liver in 
§ 1 of this chapter, we have seen reason to believe that this organ 
continues to produce sugar when the diet consists largely or exclu- 
sively of proteids. In this case we are forced to the conclusion that 
this sugar is manufactured from the elements of the non-nitrogenous 
residue. 



5° PRINCIPLES OF ANIMAL NUTRITION. 

This conclusion, based on what appears to be the normal func- 
tion of the liver, is further strengthened by a large number of ex- 
periments and observations upon the metabolism in diabetes. 
This disease, whether arising spontaneously or provoked artificially, 
is characterized by the presence of large amounts of sugar in the 
urine. It has been shown that this production of sugar continues 
when all carbohydrates are withdrawn from the diet, and further- 
more, that the amount of sugar excreted bears a quite constant 
relation to the amount of proteids metabolized, thus clearly in- 
dicating the latter as the source of the sugar. It is true that the 
formation of sugar from proteids is denied by some physiologists,* 
but by the majority it seems to be accepted as a well-established 
fact that sugar is one of the intermediate products of proteid 
metabolism. 

Of the steps of the process, as well as of its quantitative rela- 
tions, we are ignorant. In effect, it is a process of oxidation and 
hydration, since a residue of the composition computed above 
would require the addition of both hydrogen and oxygen to con- 
vert it into sugar, but that it is as simple a process as this state- 
ment would make it appear, or that the conversion is a quantitative 
one, may well be doubted. 

In conclusion it may be stated that while recent investigations 
have shown the presence of a carbohydrate radicle in numerous 
(although by no means all) proteids, it does not appear that this 
fact stands in any direct relation to the physiological production of 
sugar from these substances. In the first place, the carbohydrate 
radicle constitutes a much smaller proportion of these proteids than 
corresponds to the amount of sugar which they are apparently 
capable of yielding in the body, and in the second place it appears 
to be a well-established (although not undisputed) fact that the 
organism can produce sugar from proteids which do not contain 
the carbohydrate radicle. 

Formation of Fat. — Whether fat is formed from the elements 
of proteids in the animal body is at present a subject of controversy, 
but this question will be more profitably considered in a subsequent 
chapter. It is sufficient to remark here that while much of the 
earlier evidence bearing upon this point has been shown to be 

*Cf. Schondorf, Arch. ges. Physiol., 82, 60. 



METABOLISM. 51 

inconclusive, the formation of fat from proteids has not yet been 
disproved and has weighty direct evidence in its favor, while the 
facts that sugar may be formed from proteids, and that carbohy- 
drates are certainly a source of fat to the animal organism are 
strong additional arguments in favor of its possibility. 

Schematic Equations. — Chauveau and his associates * whose 
views regarding the functions of the carbohydrates in the body 
have already been mentioned, regard the katabolism of the proteids 
as taking place in three stages. The first consists of the splitting 
off of urea with production of carbon dioxide, water, and fat, accord- 
ing to the equation : 

4(C 72 H 112 N 18 22 S) + 1390 2 

(Stearin) 

= 2(C 57 H no 6 ) + 36CON 2 H 4 + 138C0 2 + 42H 2 + 2S 2 . 

The resulting fat is then, according to Chauveau, further oxi- 
dized in the liver, yielding dextrose, in accordance with the equation 
already given on p. 38, viz., 

2C 57 H U O 6 + 670 2 = i 6C 6 H 12 6 + 18C0 2 + 14H 2 0, 

and the dextrose is finally oxidized to carbon dioxide and water. 
Another equation representing the katabolism of proteids is that 
proposed by Gautier, which regards the first step in the process as a 
combined hydration and cleavage with the production of urea, fat, 
dextrose, and carbon dioxide, as follows : 

2(C 72 H 112 N 18 22 S)+28H 2 

(Tripalmitin) 

= 18CON 2 H 4 + 2C 51 H 98 6 + C 6 H 12 6 + 18C0 2 + S 2 . 

It may be assumed that these authors regard the above equa- 
tions simply as schematic representations of the general course of 
proteid metabolism and do not intend to imply that there are no 
intermediate stages in the process. Interpreting them in this 
sense, we have good reasons for believing that the facts which they 
represent are qualitatively true. A chemical equation, however, 
expresses not merely qualitative but quantitative results. If the 
above equations have any significance beyond that of the mere 
verbal statement that fat and sugar are products of proteid meta- 

*Cf. Kaufmann, Archives de Physiol., 1896, p. 341. 



52 PRINCIPLES OF ANIMAL NUTRITION. 

bolism, they mean that from 100 grams of proteids there is pro- 
duced, according to the first scheme, 27.61 grams of fat, and that 
from this, by the addition of oxygen, 44.67 grams of sugar are 
formed. Some of the evidence by which these equations are sup- 
ported will be considered in another connection, but may be antici- 
pated here in the statement that, in the judgment of the writer, it 
is far from sufficient to establish them as quantitative statements. 

THE NON-PROTEIDS. 

Under this comprehensive but somewhat vague term have been 
grouped all those numerous nitrogenous constituents of the food 
which are not proteid in their nature, the name being a contraction 
of non-proteid nitrogenous substances. It includes the extractives 
of meat, and in vegetable foods several groups of substances, of 
which, however, the amides and amido-acids are most abundant. 
Various substances of this class are produced by the splitting up of 
the reserve proteids in the germination of seeds and apparently 
also to some extent in the translocation of proteids in the growing- 
plant, while some at least of them appear to be produced syntheti- 
cally from inorganic materials and to be the forerunners of pro- 
teids. In young plants a considerable proportion of the so-called 
crude protein (N X 6.25) often consists of these non-proteids, and 
considerable interest, therefore, attaches to their transformations 
in the body. 

Amides Oxidized in the Body. — It has been shown by numer- 
ous investigators that various amides and amido-acids when added 
to the food are oxidized, giving rise to a production of urea. 
Shultzen & Nencki * found that glycocol, leucin, and tyrosin were 
thus oxidized, while acetamid apparently was not. So far as 
glycocol is concerned, this result is what would have been expected, 
since, as we have seen (p. 44), this body appears to be normally 
formed in the body as an intermediate product of proteid meta- 
bolism. Similar results were obtained by v. Knieriem f from 
trials with asparagin, aspartic acid, glycocol, and leucin. Munk \ 
likewise found that the ingestion of asparagin increased the pro- 

* Zeit. f. Biol, 8, 124. 

■\Ibid., 10, 277; , 36. 

JVirchow's Archiv. f. path. Anat., 94, 441. 



METABOLISM. 53 

duction of urea in the dog, all the nitrogen of the asparagin together 
with an excess over that previously found in the urine being ex- 
creted. The sulphur in the urine also increased. Hagemann * 
has more recently fully confirmed this result. Salkowski f found 
that glycocol, sarkosin, and alanin were oxidized to urea and caused 
no gain of proteids. Apparently, then, this class of bodies, like 
ammonia, furnish material out of which the organism can con- 
struct urea. 

Can Amides Replace Proteids? — Since the amides yield the 
same end products of metabolism as the proteids, it is natural to 
inquire whether they can perform any of the functions of those 
substances. 

Amides not Synthesized to Proteids. — We have already seen that 
the albumoses and peptones resulting from the cleavage of the 
proteids during digestion are built up again into proteids in the 
process of resorption. The amides commonly found in vegetable 
feeding-stuffs are likewise simpler cleavage products of the proteids, 
and some of them are also formed in digestion by the proteolytic 
action of trypsin. Can proteids be regenerated from these simpler 
cleavage products? 

If this is the case, then it should be possible, under suitable con- 
ditions, to cause a gain of proteids, or at least to maintain the 
stock of proteids in the tissues, on a food free from proteids but 
containing amides. Up to the present time, however, all attempts 
of this sort have failed. With the most abundant supply of non- 
nitrogenous nutrients and ash, the animals perished when supplied 
with amides (asparagin) but not with proteids. \ What has thus 
been found to be true of asparagin we may regard as probably true 
of other amides and say that there is no evidence that the animal 
body can build proteids from amides. 

Partial Replacement of Proteids. — But even if the amides can- 
not serve as a source of proteids to the animal, it seems not impos- 
sible that they may by their oxidation perform a part of the func- 
tions of the proteids, thus protecting a portion of the latter from 
oxidation and rendering it available for tissue production. 

*Landw. Jahrb., 20, 264. 

f Zeit. physiol. Chem., 4, 55. 

% Compare Politis, Zeit. f. Biol., 28, 492, and Gabriel, lb., 29, 115. 



54 PRINCIPLES OF ANIMAL NUTRITION. 

The earliest investigations upon this point are those of Weiske * 
and his associates upon the nutritive value of asparagin. The 
experiments were made upon rabbits, hens ; geese, sheep, and goats, 
and in the case of the two latter species included experiments on 
milk production. While the experiments are open to criticism in 
some respects, as a whole they seemed to show that asparagin, 
especially when added to a ration poor in proteids, caused a gain of 
proteids by the body. Weiske accordingly concluded that aspara- 
gin, while not capable of conversion into proteids, was capable of 
partially performing their functions and thus acting indirectly as a 
source of proteids, and this view has been somewhat generally 
accepted. Subsequent experiments by Bahlmann,f Schrodt,J 
Potthast,§ Meyer, || and Chomsky 1" upon milch-cows, rabbits, and 
sheep gave results which tended to confirm Weiske's conclusions. 

Not all of Weiske's experiments, however, gave positive results 
in favor of asparagin, and experiments upon carnivorous and omniv- 
orous animals have failed to show any such effect. In addition 
to the experiments of Politis and of Gabriel, referred to above, 
Mauthner,** Munk,f f and Hagemann \\ have failed to observe any 
gain of proteids by the body as a result of 'the ingestion of asparagin, 
but found simply an increase in the apparent proteid metabolism 
as measured by the urinary nitrogen. 

Influence on Digestion. — It can hardly be assumed that the 
actual processes of metabolism in the body tissues are fundamen- 
tally different in different species of mammals, and investigators 
have therefore been led to seek an explanation of the striking differ- 
ence in the effects of asparagin on herbivora and carnivora in the 
differences in the digestive processes of the two classes of animals. 

Digestion in herbivora is a relatively slow process and, as pointed 
out in Chapter I, is accompanied by extensive fermentations par- 

*Zeit. f. Biol., 15, 261- 17, 415; 30, 254. 

t Reported by Zuntz, Arch. f. (Anat. u.) Physiol., 1882, 424. 

JJahresb. Agr. Chem., 26, 426. 

§Arch. ges. Physiol., 32, 288. 

|| Cf. Kellner, Zeit. f. Biol., 39, 324. 

f Ber. physiol. Lab. Landw. Inst. Halle, 1898, Heft 13, p. 1. 

**Zeit. f. Biol., 28, 507. 

f f Virchow's Arch, f . path. Anat., 94, 441. 

XX Landw. Jahrb., 20, 264. 



METABOLISM. 55 

ticularly of the carbohydrates of the food, as is shown by the large 
amounts of gaseous hydrocarbons produced by these animals. In 
carnivora, on the contrary, digestion is relatively rapid and the 
dog, as a representative of this class, excretes, according to Voit & 
Pettenkofer,* but traces of hydrocarbons, and according to Tap- 
peiner,f none. 

Zuntz \ has therefore suggested that soluble amides introduced 
into the digestive canal of herbivora may be used as nitrogenous 
food by the micro-organisms there present in preference to the less 
soluble proteids, so that the latter are to a certain extent protected, 
and that it is even possible that the amides are synthesized to 
proteids by the organisms. Hagemann § has added the suggestion 
that the proteids possibly thus formed may be digested in another 
part of the alimentary canal and thus actually increase the pro- 
teid supply of the body. 

If this explanation is correct, we should expect the effect of 
asparagin to be more marked when the proportion of proteids in 
the food is small, and precisely this appears to be the case. In 
Weiske's first experiments, which gave the most decided results, 
the nutritive ratio of the ration without asparagin was 1 : 19-20, 
while a later experiment with a nutritive ratio of 1 :9.4 showed no 
effect of the asparagin upon the gain of protein. Chomsky's results, 
too, were obtained with rations poor in protein and rich in carbo- 
hydrates. 

Later experiments on lambs by Kellner |[ have fully confirmed 
this anticipation. In his first experiment two yearling lambs were 
fed with a mixture of hay, starch, and cane-sugar, having a nutri- 
tive ratio of 1 : 28, until nitrogen equilibrium was reached, when 
fifty grams of the starch was replaced by asparagin. The result 
was a gain of protein by both animals as compared with a loss in 
the first period. In the third experiment asparagin was substi- 
tuted for starch in a ration having a nutritive ratio of 1 : 7.9, and 
caused with one animal a slight gain and with the other a slight 
loss of protein. In the fourth experiment it was added to a ration 

•Zeit. f. Biol., 7, 433; 9, 2 and 438. 

flbid., 19, 318. 

J Arch. ges. Physiol., 49, 483. 

§ Landw. Jahrb., 20, 264. 

|[ Zeit. f. Biol., 39, 313. 



56 PRINCIPLES OF ANIMAL NUTRITION. 

having a nutritive ratio of 1 : 7.7, and caused neither a gain nor 
a loss of any consequence. 

Particular interest attaches to Kellner's second experiment in 
which ammonium acetate was added to a ration poor in protein 
(1:19), followed in a third period by a quantity of asparagin con- 
taining the same amount of nitrogen. The average amounts of 
protein (N X 6.25) gained per day and head by the two lambs 
were as follows : 

Basal ration 4.12 grms. 

" + ammonium acetate 15.56 " 

" " + asparagin 15.69 " 

Although it is impossible to suppose that the ammonium acetate 
is capable of performing any of the functions of proteids in the 
body, it nevertheless caused as great a gain of protein by the body 
as did the asparagin. The only obvious explanation is that both 
these substances acted in the manner suggested by Zuntz to protect 
the small amount of protein in the food from the attacks of the 
organized ferments of the digestive tract. Accepting this explana- 
tion, we must suppose that when the contents of the alimentary 
canal contain a normal amount of proteids the micro-organisms 
find an abundant supply of nitrogenous food in their cleavage 
products and reach their normal development, so that an addition 
of soluble nitrogenous substances is a matter of indifference. When,. 
on the other hand, the amount of protein present is abnormally 
low, as in Weiske's and Kellner's experiments, the organisms are 
limited in their food-supply and attack the food proteids them- 
selves. 

Kellner's results stand in apparent contradiction to the earlier 
ones of Weiske and Flechsig,* who report no gain of proteids as re- 
sulting from the addition on three days of a mixture of ammonium 
carbonate and acetate to a ration poor in protein. The excretion 
of sulphur in the urine was likewise unaffected. They assume, 
however, a long-continued after effect of the ammonium salts on the 
nitrogen excretion. If the comparison be limited to the three days 
on which the ammonium salts were given and the next following 
day, a gain of 1.15 grams of nitrogen per day results, but, as just 
stated, there was no corresponding gain of sulphur. 
*Joum. f. Landw., 38, 137. 



METABOLISM. 



57 



Kellner's experiments afford indirect evidence that both the 
asparagin and the ammonium acetate actually did stimulate the 
development of the ferment organisms, in the fact that the apparent 
digestibility of the carbohydrates of the food was increased. On 
the basal rations starch could be readily recognized in the feces, 
but under the influence of the two substances mentioned it dis- 
appeared. In the second experiment the increase in the amounts 
of crude fiber and of nitrogen-free extract digested was as follows : 

Nitrogen-free 
Crude Fiber. Extract. 

With ammonium acetate .. . 10.7 grms. 20.4 grms. 

With asparagin 10.0 " 20.0 " 

Since we know that large amounts of the nitrogen-free extract 
are attacked and decomposed by organized ferments in the her- 
bivora, and that this is the chief if not the only method by which 
crude fiber is digested, we are justified in interpreting the above 
figures as demonstrating an increased activity of these organisms 
as a result of the more abundant supply of nitrogenous food. The 
bearing of this result upon the so-called depression of digestibility 
by starch and other carbohydrates is obvious, but is aside from 
our present discussion. 

Tryniszewsky * experimented upon a calf weighing about 175 
kgs., using in the second and fourth periods (the first period being 
preliminary) a ration of barley straw, sesame cake, starch and sugar, 
containing a minimum of non-proteids. In the third period one- 
third of the sesame cake was replaced by a mixture of asparagin, 
starch and sesame oil, computed to contain an equivalent amount 
of nitrogen, carbohydrates, and fat. Owing to differences in digest- 
ibility, however, the amounts of digested nutrients, and particu- 
larly of nitrogen, varied more or less. The results of the nitrogen 
balance per 100 kgs. live weight were: 





Nitrogen Digested. 


Nitrogen 

Metabolism, 

Grms. 






Proteid, 
Grms. 


NoD-proteid, 
Grms. 


Total, 
Grms, 


Nitrogen, 
Grms. 


Period II 


72.16 
67.05 
90.86 




72.16 
90.73 
90.86 


56.86 
78.43 
76.36 


15 3 


" III 

" IV 


23.68 


12.3 
145 







Jahresb. Ag. Ch., 43, 513. 



5 8 PRINCIPLES OF ANIMAL NUTRITION. 

From the smaller gain in Period III, the conclusion: is drawn 
that the asparagin has a lower nutritive value than the proteids. 
In this period the percentage digestibility of the crude fiber 
of the ration was found to be 64.88, as compared with 43.96 and 
33.33 in the second and fourth periods, an effect corresponding to 
that observed by Kellner, and which Tryniszewsky also ascribes 
to an increase in the micro-organisms of the digestive tract. 

The results of the experiments which have been cited are, of 
course, valid, in the first instance, only for the particular non- 
proteids experimented with. If, however, the above interpretation 
of the results is correct, it is to be anticipated that other soluble 
nitrogenous substances in the food will be found to produce similar 
effects. If this anticipation proves to be correct, then we shall 
reach the following conclusions regarding the amides and similar 
bodies in feeding-stuffs. 

1. That they do not serve as sources of proteids. 

2. That in rations very poor in protein they have, in the her- 
bivora, an indirect effect in protecting part of the food protein 
from fermentation in the digestive tract. 

3. That in carnivora, and in herbivora on normal rations, they 
probably have no effect on the production of nitrogenous tissue. 



CHAPTER III. 
METHODS OF INVESTIGATION. 

An essential prerequisite for an intelligent study of the income 
and expenditure of matter by the animal body is a knowledge of 
the general nature of the current methods of investigation and of 
the significance of the results attained by means of them. It is 
not the purpose here to enter into technical details; this is not 
a treatise upon analytical or physiological methods. The present 
chapter will be confined to outlining the general principles upon 
which those methods are based and to pointing out the logical 
value of their results. It will be confined, moreover, mainly to 
those general methods by which the balance of income and ex- 
penditure of matter is determined. 

Tissue. — The animal body has already been characterized as 
consisting, from the chemical point of view, of an aggregate of 
various substances, chiefly organic, representing a certain capital 
of matter and energy. These various substances are grouped 
together in the body to form the organized structures known as 
tissues. For the sake of brevity, then, it may be permissible to use 
the word tissue as a convenient general designation for the aggre- 
gate of all the organic matter contained in the tissues of the body, 
including both their organized elements and any materials present 
in the fluids of the body or in solution in the protoplasm of the 
cells. In this sense tissue is equivalent to the whole capital or 
store of organic matter in the body. 

Gains and Losses. — The tissue of the body, as thus defined, is 
in a constant state of flux, the processes through which the vital 
functions are carried on constantly breaking it down and oxidizing 
it (katabolism), while the processes of nutrition are as constantly 
building it up again (anabolism). If the activity of nutrition 

59 



60 PRINCIPLES OF ANIMAL NUTRITION. 

exceeds that of destruction, material of one sort or another is stored 
up in the body, and such an addition to its capital of matter and 
energy we may speak of as a gain of tissue. Conversely, if the 
katabolic processes consume more material than the processes of 
nutrition can supply, the store of matter and energy in the body 
is diminished and a loss of tissue occurs. A simple comparison of 
the amount of matter supplied in the food (including, of course, 
the oxygen of the air) with that given off in the solid, liquid and 
gaseous excreta, therefore, will show whether the body is gaining 
or losing tissue. 

The mere fact of a gain or loss of matter by the body, however, 
conveys but little useful information unless we know the nature of 
the material gained or lost. This we have no means of determining 
directly. The processes of growth or decrease are not accessible 
to immediate observation, while changes in the weight of the animal 
(even aside from the great uncertainties introduced, especially in 
the herbivora, by variations in the contents of the alimentary 
canal) represent simply the algebraic sum of the gains and losses 
of water, ash protein, fats, and other materials, and so give but a 
very slight clue if any to the real nature of the tissue-building. We 
are compelled, therefore, to have recourse to indirect methods, and 
to base our conclusions as to tissue-building upon a comparison 
of the income and outgo of the chemical elements of which the body 
is composed, particularly of nitrogen and carbon. 

The Schematic Body. — The basis of this method of compari- 
son is the conception of the schematic body, first introduced by 
Henneberg.* This conception regards the dry matter of the body 
of the animal as composed essentially of three groups of substances, 
viz., ash, fat, and protein, with at most comparatively small amounts 
of carbohydrates (glycogen), and assumes that the vast number of 
other compounds which it actually contains are present in such 
small and relatively constant proportions as not to materially 
affect the truth of this view. A knowledge of the ultimate compo- 
sition of these three groups then affords the basis for a computation 
of the gain or loss of each from the income and outgo of their ele- 
ments. 

Ash. — The ash ingredients of the body form a well-defined 

* Neue Beitrage, etc., p. vii. 



METHODS OF INVESTIGATION. 



61 



group, and the determination of the gain or loss of each ingredient 
from a comparison of income and outgo is in principle a relatively 
simple matter and calls for no special consideration here. 

Fat. — The elementary composition of the fat of the body has 
been shown to be remarkably similar not only in different animals 
of the same species, but likewise in different species. The classic 
investigations of Schulze & Reinecke* upon the composition of 
animal fat gave the following results: 



Beef fat. . . 
Pork fat.., 
Mutton fat 

Average 

Dog 

Cat 

Horse 

Man 



No. of 
Sam- 
ples. 



10 
6 

12 



28 



Carbon. 



Aver- 
age 
Per 

Cent. 



76.50 
76.54 
76.61 



76.50 

76.63 
76.56 

77.07 
76.62 



Maxi- 
mum 
Per 



Mini- 
mum 
Per 



Cent. Cent. 



76.74 76.2711 

76.78 

76.85 



Hydrogen. 



Aver- 
age 
Per 

Cent. 



91 
76.29 11.94 
76.2712.03 



12.00 

12.05 
11.90 
11.69 
11.94 



Maxi- 
mum 
Per 
Cent. 



12.11 
12.07 
12.16 



Mini- 
mum 
Per 

Cent. 



11.76 
11.86 
11.87 



Oxygen. 



Per 
Cent. 



11.59 
11.52 
11.36 



11.50 

11.32 
11.44 
11.24 

11.44 



Maxi- 
mum 
Per 
Cent. 



11.86 
11.83 
11.56 



Mini- 
mum 
Per 
Cent. 



11.15 



Benedict and Osterberg f obtained the following results for the 
composition of human fat: 



Sample No. 1 

" 2 

" 3 

" 4 

" 5 

" 6 

" 7 



Average 



76.08 



Carbon, 


Hydrogen, 


Per Cent. 


Per Cent. 


76.29 


11.80 


76.36 


11.72 


75.85 


11.87 


75.95 


11.85 


75.94 


11.74 


76.07 


11.69 


76.13 


11.84 


76.05 


11.81 



11.78 



The fat of the body has been commonly regarded as containing 
76.5 per cent, of carbon. A gain of 100 parts of fat by the body 



*Landw. Vers. Stat., 9, 97. 



f Amer. Jour. Physiol., 4, 69. 



62 



PRINCIPLES OF ANIMAL NUTRITION. 



is accordingly equivalent to a gain of 76.5 parts of carbon, and con- 
versely, if it be shown that the body has gained one part of carbon 
in the form of fat, this is equivalent to a gain of 1-^-0.765=1.307, 
or, in round numbers, 1.3 parts of fat. Benedict & Osterberg's 
average corresponds to the factor 1.314. 

Protein. — As in the case of the food, the term protein is used 
to signify the whole mass of nitrogenous material in the body, in- 
cluding, besides the true albuminoids, the collagens or gelatinoids, 
the keratin-like bodies, the nitrogenous extractives, etc. 

Neumeister * gives the following figures for the elementary 
composition of the simple albuminoids: 





Minimum, 
Per Cent. 


Maximum, 
Per Cent. 


Average, 
Per Cent. 




50 

6.5 
15 
19 

0.3 


55 

7.3 
17.6 
24 

2.4 


52 

7 

16 

23 

2 










100 



Some of the compound albuminoids, particularly the nucleo- 
albuminoids, do not vary greatly in composition from the above 
figures, while others notably the mucins, which contain a carbo- 
hydrate group, show a higher percentage of oxygen and less carbon 
and nitrogen. 

The gelatinoids, likewise, do not differ greatly in composition 
from the albuminoids. For collagen, Hofmeister f found the fol- 
lowing averages: 

Carbon; 50.75 

Hydrogen 6 . 47 

Nitrogen 17.86 

Oxygen | 24.91 

Sulphur ) 

100.00 
Keratin is distinguished by a relatively high proportion of 
sulphur (3 to 5 per cent.), but otherwise, according to Neumeister, \ 
does not differ materially in composition from the true albuminoids. 
*Lehrbuch der Physiol. Chem., p. 22. fZeit. physiol. Chem., 2, 322. 
JLoc cit., p. 493. 



METHODS OF INVESTIGATION. 



63 



Hoppe-Seyler * quotes the following figures for the composition 
of epidermis and some of the tissues derived from it : 





Epidermis 
of Man. 


Hair. 


Nails. 


Horn of 
Cow. 


Hoof of 
Horse. 




50.28 

6.76 

17.21 

25.01 

0.74 


50.65 

6.36 

17.14 

20.85 

5.00 


51.00 

6.94 

17.51 

21.75 

2.80 


51.03 

6.80 

16.24 

22.51 

3.42 


51.41 
6 96 






17 46 




19 49 




4 23 








100.00 


100.00 


100.00 


100.00 


99.55 (?) 



flenneberg f obtained the following figures for the composition of 
two samples of pure and dry wool, calculated ash-free: 

I. IT. 

Carbon 49.67 49.89 

Hydrogen 7.26 7.36 

Nitrogen 16.01 16.08 

Oxygen 23.65 23.10 

Sulphur 3.41 3.57 

100.00 100.00 

The following analyses by Rubner,t Stohmann & Langbein,§ 
and Argutinsky|| show the ultimate composition of ash-free muscular 
tissue after prolonged extraction with ether : % 



Carbon, 
Per Cent. 



Hydro- 
gen, 
Per Cent. 



Nitrogen, 
Per Cent, 



Sulphur, 
Per Cent. 



Oxygen, 
Per Cent. 



Heat of 
Com- 
bustion 
perGram, 
Cals. 



Rubner 

Stohmann and Langbein. 
Argutinsky 



53.40 
52.02 
52.33 



7.30 
7.30 



16.30 
16.36 
16.15 



24.32 
24.22 



5.6561 
5.6409 



* Physiol. Chem., p. 90. fNeue Beitrage, etc., p. 98. 

JZeit. f. Biol., 21, 310. §Jour. f. prakt. Chem., N. F., 44, 364. 

|| Arch. ges. Physiol., 55, 345. 

1[It has since been shown by Dornmeyer (Arch. ges. Physiol., 65, 90) 
that such material is not fat- free 



6 4 



PRINCIPLES OF ANIMAL NUTRITION. 



Kohler* has investigated the elementary composition of the 
muscular tissue of cattle, sheep, swine, horses, rabbits and 
hens. The material was prepared with much care, the fat being 
removed as fully as possible by prolonged extraction with ether. 
The residual fat which cannot be removed in this way was deter- 
mined by Dornmeyer's digestion method,f and a corresponding 
correction made in the analytical results. The following are his 
averages for the fat- and ash-free substance : 





No. of 
Samples. 


Carbon, 
Per Cent. 


Hydrogen, 
Per Cent. 


Nitrogen, 
Per Cent. 


Sulphur, 
Per Cent. 


Oxygen, 
Per Cent. 


Heat of 

Combustion 

per Gram, 

Cals. 




4 
2 
2 
3 
2 
2 


52.54 
52.53 
52.71 
52.64 
52.83 
52.36 


7.14 
7.19 
7.17 
7.10 
7.10 
6.99 


16.67 
16.64 
16 60 
15.55 
16.90 
16.88 


0.52 
0.69 
0.59 
0.64 


23.12 
22.96 
22.95 

24.08 


5.6776 

5.6387 
5.6758 
5.5990 
5 6166 


Hen 


0.50 


23.28 


5.6173 



All the samples were tested for glycogen, but only traces were 
found, except in the horseflesh, for the two samples of which an 
average of 3.65 per cent, was obtained, a result which accounts for 
the low figure for nitrogen. 

In the classic investigation by Lawes & Gilbert % into the com- 
position of the whole bodies of animals, determinations were made 
of the total dry matter, the ash, the fat, and the total nitrogen. 
From these data Henneberg § has compared the total amount of 
dry matter other than ash and fat with the total amount of nitro- 
gen. His results in a slightly altered form are given in the table 
opposite. 

The average nitrogen content is 16.21 per cent. Lawes & Gil- 
bert extracted the fat with ether and hence, as above noted, the 
residue was not absolutely fat-free. Kohler's average results for the 



* Zeit. physiol. Chem., 31, 479. 
t Arch. ges. Physiol, 65, 102. 
J Phil. Trans., 1859, II, 493. 
§Neue Beitrage, etc., p. x. 



METHODS OF INVESTIGATION. 



65 





Ox. 


Sheep. 


Swine. 




Half Fat, 
Per Cent. 


Fat, 
Per Cent. 


Lean, 
Per Cent. 


Fat, 
Per Cent. 


Lean, 
Per Cent. 


Fat, 
Per Cent. 




56.1 
43.9 


48.6 
51.4 


61.0 
39.0 


46.2 
53.8 


58.2 

41.8 


42.9 




57.1 






In the dry matter : 
Ash 


100.00 

5.1 
20.7 

18.1 


100.00 

4.1 
31.9 

15.4 


100.00 

3.4 
19.9 

15.7 


100.00 

2.9 
37.9 

13.0 


100.00 

2.8 
24.6 

14.4 


100.00 
1.7 


Fat 


44.0 


Other organic matter 


11.4 




43.9 
3.0 

16.58 


51.4 

2.4 

15.59 


39.0 
2.55 
16.24 


53.8 

2.1 

16.19 


41.8 

2.3 

15.97 


57.1 
1.9 


Per cent, of nitrogen in 
"other organic matter" 


16.66 



flesh of cattle, sheep, and swine, after extraction with ether for 

480 hours, computed ash-free, were: 

Carbon 52.84 

Hydrogen 7 . 22 

Nitrogen 16.46 

Oxygen 22 . 89 

Sulphur 0.59 

100.00 

Considering the indirect method by which Henneberg's result 
was reached, the agreement as regards nitrogen, both with Kohler's 
results and with those of Rubner, Stohmann, and Argutinsky just 
cited, is remarkably close. Henneberg assumed the following 
round numbers to represent the average composition of the total 
protein of the body, and his example has been generally followed 
by subsequent investigators: 

Carbon 53 per cent. 

Hydrogen 7 

Nitrogen 16 " " 

Oxygen 23 " 

Sulphur 1 " " 

100 



66 PRINCIPLES OF ANIMAL NUTRITION. 

Kohler's averages for dry, fat-free flesh are: 

Carbon 52 . 60 per cent. 

Nitrogen 16.67 " " 

Glycogen. — Of the substances other than ash, fat and protein, 
which are found in the animal body, only glycogen calls for special 
mention here. This body, as we have seen, may be stored up in 
considerable amounts in the liver, and is found also in the muscles, 
although not in large proportion, except in case of the horse. In 
the aggregate, however, the store of glycogen in the body is not 
inconsiderable, having been estimated to be in the neighborhood 
of 300 grams in the human body. Moreover, changes of food or 
conditions, as well as muscular activity, may materially alter the 
store of glycogen and thus, perhaps, appreciably affect the make- 
up of the schematic body. 

So far as appears, however, the capacity of the body to store up 
glycogen is limited, as is indicated by the relatively small amount 
of it formed after even the most abundant feeding, and we may 
fairly assume that, at least on a ration equal to or exceeding the 
maintenance requirements, no long-continued change in the amount 
of glycogen in the body is likely to occur. 

Summary. — We may sum up the foregoing paragraphs in the 
brief statement that for the purpose of investigating the statistics 
of nutrition we may consider the organic part of the animal body 
as composed essentially of fat and protein, with small amounts of 
glycogen, and that we may regard the permanent effect of a ration 
upon the body as consisting (aside from its effect on the ash ingre- 
dients) in an increase or decrease of its stores of fat and protein, 
these substances having the average compositon indicated above. 
The Gain or Loss of Protein. — Since the term protein as here 
used is synonymous with total nitrogenous matter, the gain or loss 
of protein by the body is necessarily indicated by its gain or loss of 
nitrogen. 

The supply of nitrogen to the body is contained in the pro- 
tein of the food. The losses of nitrogen from the body are 
contained — 

First, in that part of the protein of the food which fails of 
digestion and is excreted in the feces. 



METHODS OF INVESTIGATION. 6 J 

Second, in the nitrogenous products of the proteid metabolism, 
contained chiefly in the urine but including also the small quanti- 
ties of nitrogenous metabolic products contained in the feces and 
perspiration. 

The nitrogen of urine and perspiration, then, together with the 
metabolic nitrogen of the feces, will indicate the extent of proteid 
katabolism, while the difference between total income and total 
outgo of nitrogen will show whether the body is gaining or losing 
protein. Finally, since the losses of metabolic nitrogen in feces and 
perspiration are relatively small, and often not readily determinable, 
in cases where the greatest accuracy is not required, and particularly 
in comparative experiments, we may regard the total urinary nitro- 
gen as representing with a fair degree of accuracy the amount of 
protein broken down by the organism. 

In the foregoing statements, however, it has been tacitly assumed 
that the protein of the food consists of true proteids. If, how- 
ever, the latter are accompanied by amides and other non-proteid 
nitrogenous bodies, which do not appear to contribute to the forma- 
tion of proteid tissue (compare p. 53), the corresponding amount 
of nitrogen will appear in the urine and be added to that derived 
from the actual katabolism of body or food proteids. This, how- 
ever, does not, of course, affect any conclusions as to the gain or loss 
of protein by the body. 

Factor for Protein. — It is thus comparatively easy to deter- 
mine in terms of nitrogen both the proteid katabolism and the 
gain or loss of protein, the principal precaution necessary, aside 
from technical details, being that the experiment shall extend over 
a sufficient length of time to eliminate the influences of irregulari- 
ties in ingestion and excretion. 

Knowing approximately the ultimate composition of the pro- 
tein of the body, we may take a step further and infer from the 
amounts of nitrogen determined the corresponding amounts of 
protein, the accuracy of the result depending, of course, upon the 
accuracy of the figures on which it is based. The composition 
commonly assumed for the body protein has been that given on 
page 65, and the same conventional factor, 6.25, has been used 
to convert nitrogen into protein which has been employed in case 
of feeding-stuffs. Kohler's investigations (p. 64) show that the 



68 PRINCIPLES OF ANIMAL NUTRITION. 

nitrogenous organic matter of muscular tissue has a materially 
higher percentage of nitrogen, viz., about 16.67 per cent. This 
would reduce the factor for protein from 6.25 to 6.00. Kohler's 
samples, after extraction with ether for 480 hours, still contained 
from 0.27 to 1.61 per cent, of fat. If we assume the ash and 
fat-free substance of Lawes & Gilbert's experiments (p. 65) to 
have still contained 1 per cent, of fat, the average nitrogen con- 
tent of the fat-free substances would be 16.38 per cent, and the 
corresponding protein factor 6.11, while the factor 6.00 would re- 
quire the assumption of a fat-content of 2.7 per cent. 

The factor 6.0 has been used by Kellner in computing the results 
of his extensive investigations upon cattle at Mockern. Strictly 
speaking, this assumes that all the gain of nitrogen takes place 
either in the form' of muscular tissue or of material of the same 
average composition. To what extent such an assumption is 
justified it is difficult to say. Certainly a part of the protein of the 
food is applied to the production of epidermis, hair, horns, hoofs, 
etc., consisting largely of keratins. The data regarding the com- 
position of these tissues given on p. 63 would seem to show 
that they are, on the average, richer in nitrogen than muscular 
tissue, a fact which would tend to lower the protein factor, but on 
the other hand, the amount of this growth is small as compared 
with the usual protein supply. On the whole, Kohler's factor 
would seem to afford the most trustworthy basis of computation 
which is at present available, especially in view of its close agree- 
ment with Lawes & Gilbert's results. 

Urea as a Measure op Proteid Metabolism. — In the earlier 
investigations upon this subject, the urea of the urine, as deter- 
mined by Liebig's titration method, was commonly taken as the 
measure of proteid metabolism, one part of urea equaling 2.9 parts 
of protein, while in many cases the metabolism was also expressed 
in terms of " flesh " (muscular tissue) with its normal water con- 
tent and an average of 3.4 per cent, of nitrogen. The errors inci- 
dent to the use of this method are now generally recognized, while 
its inapplicability to herbivora was obvious from the first, and with 
the improvements in the methods of nitrogen determination, the 
latter has almost entirely replaced the old urea determination and 



METHODS OF INVESTIGATION. 69 

the proteid metabolism is now almost exclusively expressed in 
terms of either nitrogen or protein. 

The Gain or Loss of Fat. — As the balance between income 
and outgo of nitrogen serves to measure the gain or loss of protein 
by the schematic body, so the balance between income and outgo 
of carbon furnishes the means for estimating the gain or loss of fat. 

The income of carbon is, of course, the carbon of the food. 
The outgo of carbon consists of — 

First, the carbon of the undigested food contained in the feces. 

Second, the carbon of the products of metabolism contained 
in feces, urine, and perspiration. 

Third, the carbon of the gaseous excreta, including the carbon 
dioxide given off by the lungs and skin and the carbon dioxide and 
hydrocarbons resulting from fermentations in the digestive tract. 

Respiration Apparatus. — The carbon of the visible excreta 
is readily determined by the ordinary analytical methods. The 
determination of the carbon of the gaseous excreta requires the use 
of a special apparatus, commonly called a respiration apparatus. 

In early experiments upon respiration the animal was simply 
placed in a known confined volume of air which was analyzed before 
and after the experiment. By this method, however, the oxygen 
of the air is progressively diminished, while the respiratory products 
accumulate, both of which conditions are liable to disturb the 
normal respiratory exchange, although Kaufmann,* who has re- 
cently reverted to this primitive method, claims to have secured 
accurate results in rather short experiments. 

The obvious desirability of renewing the oxygen and removing 
the products of respiration soon led to the construction of more 
complicated forms of apparatus of which three principal types 
may be distinguished. 

The Regnault Apparatus. — The oldest of these is the Regnault f 
or closed circuit respiration apparatus. In this type of apparatus 
the subject breathes in a confined volume of air, the carbon dioxide 
being removed by suitable absorbents and weighed, while the oxy- 
gen consumed is replaced from a receiver containing pure oxygen, 
the amount admitted to the apparatus being measured. These 

* Archives de Physiol., 1896, p. 329. 

f Regnault & Reiset, Ann. de Chim. et de Physique, 3d series, 26, 299. 



70 PRINCIPLES OF ANIMAL NUTRITION. 

data, with the addition of analyses of the known volume of air 
contained in the apparatus at the beginning and end of the 
experiment, afford the means of computing both the carbon dioxide 
and other gases given off and the oxygen cousumed.* 

In theory this is the most complete and satisfactory type of 
respiration apparatus, since it permits a determination of the total 
gaseous exchange. Serious practical difficulties have been found 
in its use, however, especially for the larger animals, among them 
the difficulty of maintaining the air reasonably pure, the difficulty 
of securing a uniform temperature and mixture of the gases in a 
large and complicated apparatus, and the liability to contamination 
of the oxygen used. Seegen & Nowak f used an apparatus of 
this type for their experiments upon the excretion of gaseous nitro- 
gen by animals (see p. 42). Laulanie J has described a Regnault 
apparatus for small animals in which a continuous graphic measure- 
ment of the oxygen admitted to the apparatus is made, Hoppe- 
Seyler § has constructed at Strasburg an apparatus of this type 
large enough to contain a man, and Bleibtreu || has recently made 
use of a small one to investigate the formation of fat in geese, but 
the apparatus has not come into general use.^T 

The Pettenkofer Apparatus. — The second type of respiration 
apparatus is that of v. Pettenkofer. In this type the subject 
breathes in a closed chamber through which a measured current 
of air is maintained. 

Scharling ** appears to have been the first to construct an appa- 
ratus of this sort. The ingoing air was freed from carbon dioxide 
by passing through potash solution, while the outcoming air, after 
drying, gave up its carbon dioxide to a weighed potash bulb. Vari- 
ous similar forms of apparatus were constructed, but it was found 

* For a description of the apparatus, see also Hoppe-Seyler, Physiol. 
Chem., pp. 526 and 536. 

t Sitzungsber. Wiener Akad., Math.-Naturwiss. Classe, 71, III, 329; 
Arch. ges. Physiol., 19, 349. 

| Archives de Physiol., 1890, p. 571. 

§Zeit. physiol. Chem., 19, 574. 

|| Arch. ges. Physiol., 85, 366. 

IT See also Pfliiger and Colasanti (Arch. ges. Physiol., 14, 92) and Schulz 
</&., p. 78). 

**Ann. Chem. Pharm., 45, 214. 



METHODS OF INVESTIGATION. 7 1 

to be impossible to secure complete absorption of the carbon dioxide 
and at the same time maintain adequate ventilation. 

In 1862 v. Pettenkofer* introduced the important improve- 
ment of diverting a known aliquot of both the ingoing and outcom- 
ing air for analysis. The results of these analyses, calculated upon 
the whole volume of air used, show the amounts of carbon dioxide 
and other gases added by the subject of the experiment. 

The Pettenkofer apparatus has the advantage of placing the 
subject under unquestionably normal conditions as to purity of 
air, of maintaining a practically uniform temperature and mixture 
of gases throughout the apparatus, and of dispensing with the ex- 
treme care necessary in the Pegnault apparatus to prevent gaseous 
diffusion between the air outside and that inside the apparatus. 
Its great drawback is that it does not in practice permit the deter- 
mination of the amount of oxygen consumed.f To this is to be 
added the magnification of experimental errors involved in com- 
puting the results obtained by the analysis of small samples upon 
the whole volume of air used. 

Despite these drawbacks, however, the Pettenkofer apparatus 
in various forms has been widely used, especially in experiments 
upon domestic animals, and has shown itself capable of yielding 
very accurate results within its scope. Laulanie,J by largely re- 
ducing the rate of ventilation, has been able to make determinations 
of the oxygen consumed which he regards as satisfactory, while 
Haldane § has constructed an apparatus for small animals, in which 
the entire air current is passed over absorbents before entering 
and after leaving the apparatus, which also permits of a satisfac- 
tory indirect determination of the oxygen consumed. Sonden and 
Tigerstedt | have also constructed a modified Pettenkofer respira- 

* Ann. Chem. Pharm., Suppl. Bd. II, p. 1. See also Atwater, U. S. Dep. 
Agr., Office of Experiment Stations, Bull. 21, p. 106. 

f Such a determination is theoretically possible from a comparison of the 
oxygen content of ingoing and outcoming air, but the delicacy of the measure- 
ments and analyses required is so great as to render the method impracti- 
cable, while the determination by difference concentrates all the errors in 
this one quantity. 

% Archives de Physiologie, 1895, p. 619. 

§Jour. Physiol., 13, 419. 

|| Skand. Arch. Physiol., 6, 1. 



7 2 



PRINCIPLES OF ANIMAL NUTRITION. 



tion apparatus of very large dimensions. Recently Atwater & 
Rosa * have constructed a form of Pettenkofer apparatus for use 
as an animal calorimeter in which the method of measuring and 
sampling the air current has been materially improved and rendered 
more accurate. 

When the Pettenkofer apparatus is employed for experiments 
upon herbivora, special provision is necessary for the determination 
of the gaseous hydrocarbons excreted in considerable quantities 
by these animals. This is accomplished by passing a sample of the 
air coming from the apparatus through a combustion-tube contain- 
ing copper oxide, or preferably spongy platinum (platinized kaolin), 
heated to redness. The hydrocarbons are thus oxidized and the 
resulting carbon dioxide determined. 

Pettenkofer & Voit,f in their earlier investigations, deter- 
mined the excretion of combustible gases by a dog, with the follow- 
ing results per day: 



Food. 


Hydrogen, 
Grams. 


Methane, 
Grams. 


Carbon 


Meat, 
Grams. 


Fat, 
Grams. 


Starch, 
Grams. 


Dioxide, 
Grams. 


500 




200 

200 
200 


7.2 
5.2 
7.2 
6.4 
4.3 


4.1 
6.3 

4.7 
3.7 
4.5 


416.0 


500 




420.6 


500 




428.2 


500 
500 


200 
200 


417.3 

427.8 







According to the above figures, a trifle less than 3 per cent., 
on the average, of the total carbon excretion was in the form of 
methane. No similar determinations seem to have been made by 
Pettenkofer & Voit in their later experiments, and it appears to 
be generally assumed that they are unnecessary in investigations 
upon man and the carnivora. 

The Zuntz Apparatus. — Both the Regnault and the Pettenkofer 
types of apparatus are calculated for the determination of the 
total gaseous excreta of lungs, skin, and digestive tract through 
considerable periods of time, and their use enables us to compare 
the total income and outgo of carbon. 

* U. S. Dept. Agr., Office of Experiment Stations, Bulletins 44 and 63. 
t Ann. Chem. Pharm., Supp. Bd. II, p. 66. 



METHODS OF INVESTIGATION. 73 

The third type of respiration apparatus is best known by the 
name of Zuntz,* from the extensive development given it by this 
investigator,, although it has assumed various forms in the hands 
of different experimenters. This apparatus is radically different 
from the other two types in that it is intended simply for the deter- 
mination of the respiratory exchange in the lungs. For this pur- 
pose the expired air is collected, either by means of a mask or a 
tracheal cannula, its volume measured, and its content of carbon 
dioxide and of oxygen determined in an aliquot sample, the com- 
position of the inspired air being assumed to be that of the normal 
atmosphere. The fundamental principle is really that of the Petten- 
kofer apparatus, but, owing to the fact that the excretory gases 
are not diluted with many times their volume of air, the results are 
much sharper and it is possible to determine the amount of oxygen 
consumed as well as of the carbon dioxide given off. In addition 
to this advantage, it permits the experimenter to follow the varia- 
tions in the respiratory exchange in comparatively short periods. 
It is thus especially adapted for investigating such questions as the 
influence of muscular work upon metabolism, and it is in the study 
of this question that it has found its chief application. On the 
other hand, it is impracticable to continue its use through long 
periods — a day, e.g. — and it takes no account of the excretion 
through the skin and the alimentary canal. Only by indirect 
methods, therefore, is it possible to compute the total income and 
outgo of carbon by its use. 

But while the Zuntz form of respiration apparatus is especially 
adapted for investigating the carbon metabolism during short 
periods, it is important that these periods be not made too short. 
What is actually determined by the use of any form of respiration 
apparatus is the excretion or absorption of carbon dioxide or oxy- 
gen. In an experiment extending over several hours, we may 
fairly assume that this is substantially a measure of the actual pro- 
duction or consumption of these gases going on in the tissues. In 
periods of a few minutes, however, there is always a possibility of 
an accumulation of oxygen or a partial retention of the products 
of metabolism in the tissues or the blood, while, on the other hand, 

*Rohrig & Zuntz, Arch. ges. Physiol., 4, 57; v. Mehring & Zuntz, ib., 32, 
173; Geppert & Zuntz, ib., 42, 189. 



74 PRINCIPLES OF ANIMAL NUTRITION. 

the products of previous metabolism may be added to those formed 
during the experiment. This is especially true of the carbon diox- 
ide, particularly in work experiments, where the rate and volume 
of respiration are largely affected. During severe work, there may 
be more or less accumulation of this gas in the blood, while, on the 
other hand, the increased respiration in an immediately following 
period of rest may reduce the proportion in the blood below the 
normal. The oxygen is thought to be far less subject to this error 
than the carbon dioxide, and therefore to be a more accurate indi- 
cator of the total metabolism. 

The Respiratory Quotient. — This name was given by Pfltiger 
to the ratio of the volume of carbon dioxide excreted to the volume 
of oxygen consumed in the same time. It is frequently represented 

CO 

by the abbreviation R.Q., or by the symbol -~- 2 . 

It is obvious that this ratio will vary with the nature of the 
material metabolized. Thus the oxidation of a carbohydrate, e.g. 
dextrose, will give rise to a volume of carbon dioxide equal to that of 
the oxygen consumed, since, as the following equation shows, each 
molecule of oxygen gives rise to a molecule of carbon dioxide: 

C fi H 12 6 + 60 2 = 6C0 2 + 6H 2 0. 

In this case the respiratory quotient is equal to unity. On the 
other hand, when fat is oxidized, a portion of the oxygen combines 
with the hydrogen of the fat to form water, and the volume of car- 
bon dioxide produced is less than that of the oxygen employed. 
Representing the process by the equation used by Chauveau,* viz., 

2C 57 H 110 O 6 + 1630 2 = 114C0 2 + 110H 2 O, 

114 

the respiratory quotient is ^5 = 0.6993. Computed from the aver- 
age percentage composition of animal fat as given on p. 61, it 
equals 0.7069. 

The proteids of the food, as we have seen, are not completely 
oxidized in the body, a portion of their carbon, along with all their 
nitrogen, being excreted in the form of urea and other organic 

*La Vie et l'Energie chez l'Animale. 



METHODS OF INVESTIGATION. 75 

compounds in the urine. Chauveau & Kaufmann,* starting with 
an empirical formula for albumin, represent its complete meta- 
bolism in the body by the equation 

2C 72 H 112 N 18 22 S 2 + 1510 2 = 18CH 4 N 2 + 126C0 2 + 76H 2 + S 2 , 

126 
thus obtaining the respiratory quotient — = 0.8344, neglecting 

the oxygen required to oxidize the sulphur. 

The urine, however, always contains greater or less quantities 
of nitrogenous compounds richer in carbon than urea, and in herbiv- 
orous animals in particular such compounds are abundant. The 
respiratory quotient of the proteids is therefore variable, depend- 
ing upon the extent to which their carbon is completely oxidized. 
Thus Zuntz and Hagemannf in an experiment upon the horse 
in which approximately 15 per cent, of the total nitrogen of the 
urine was contained in hippuric acid, compute it at 0.765. 

Deductions from Respiratory Quotient. — The value of a determi- 
nation of the respiratory quotient lies in the clue which it affords to 
the nature of the substances which are being oxidized in the body. 
Assuming that the materials available for oxidation in the schematic 
body are substantially proteids, carbohydrates and fat, it is evi- 
dent that when the quotient approaches 1.0 the material consumed 
must consist largely of carbohydrates, while if it falls to the neigh- 
borhood of 0.7 it is clear that the oxygen is combining chiefly with 
fat. An intermediate value, on the other hand, would be more am- 
biguous, since it might result from the oxidation of proteids, carbo- 
hydrates and fat in several proportions. 

If, however, the amounts of oxygen consumed and of carbon 
dioxide produced in the oxidation of any one of the three groups be 
known, it is a simple matter to compute the proportion in which 
the other two enter into the reaction. For the amount of proteids 
metabolized, we have an approximate measure in the total urinary 
nitrogen. If we can also determine the amounts of carbon, hydro- 
gen and oxygen contained in these nitrogenous urinary products, 
we can compute the quantity of oxygen required to oxidize the non- 
nitrogenous residue of the proteids and the amount of carbon diox- 
ide resulting from it. upon the assumption of complete oxidation. 

* Compare p. 51. fLandw. Jahrb., 27, Supp. Ill, 240. 



76 PRINCIPLES OF ANIMAL NUTRITION. 

As a matter of fact, however, it is not easy to determine satis- 
factorily the proportion of the respiratory exchange clue to the 
proteids, both because the nitrogenous products of their meta- 
bolism are numerous and occur in varying proportions in the urine, 
and because we may not always be justified in assuming complete 
oxidation of the non-nitrogenous residue. Computations of the 
nature indicated above, therefore, must be accepted with some 
reserve. 

A simpler case, and one which has been extensively investigated, 
is the nature of the increased metabolism arising from muscular 
exertion. As we shall see in a succeeding chapter, such exertion 
causes a marked increase in the respiratory exchange while pro- 
ducing at most but a slight effect upon the proteid metabolism. 
If we neglect altogether this latter effect, the ratio between the in- 
crements of carbon dioxide and oxygen will indicate whether the 
additional material consumed during the performance of the work 
consisted of fat or carbohydrates or a mixture of the two, of course 
on the same assumption as before, viz., that substantially only 
these two classes of substances are available in the schematic body. 

For example, in an investigation by Zuntz, cited on a subsequent 
page, the performance of one kilogram-meter of work of draft 
by a dog caused the following increments in the respiratory ex- 
change : 

Oxygen 1 . 6704 c.c. 

Carbon dioxide 1.4670 " 

Respiratory quotient . 878 

Assuming, as above, that these amounts arise from the oxida- 
tion of fat and carbohydrates only, let x equal the amount of oxy- 
gen consumed in the oxidation of fat and 1.6704 — a: the amount 
consumed in the oxidation of carbohydrates. Since the respira- 
tory quotient of fat is 0.7069, the x cubic centimeters of oxygen 
would yield 0.7069a; cubic centimeters of carbon dioxide, while the 
1.6704— a: cubic centimeters of oxygen used to oxidize the carbohy- 
drates would yield an equal volume of carbon dioxide. We there- 
fore have — 

. 7069z +( 1 . 6704 - x) = 1 . 4670, 
whence x= 0.6939. 



METHODS OF INVESTIGATION. 77 

The division of the increments of the respiratory gases was accord- 
ingly— 

Oxygen Carbon Dioxide 

Consumed. Produced. 

By fat 0.6939 c.c. 0.4905 c.c. 

By carbohydrates . . 9765 " . 9765 " 

it 

Total 1.6704 " 1.4670 " 

From these data the actual amounts of fat and carbohydrates 
metabolized can be readily computed, one gram of fat requiring for 
its oxidation 2.8875 grams (2.028 liters) of oxygen and producing 
1.434 liters of carbon dioxide, while one gram of a carbohydrate of 
the composition of starch requires 1.185 grams (0.832 liter) of 
oxygen and produces the same volume of carbon dioxide. 

Computation of Fat from Carbon Balance. — While the use 
of the Zuntz type of respiration apparatus may afford invaluable 
information regarding the nature of the chemical changes going 
on in the body, a satisfactory determination of the gain or loss of 
carbon by the body usually requires the employment of one of the 
other types of apparatus.* Having by such means added a deter- 
mination of the carbon balance to that of the nitrogen balance, we 
have the data necessary for computing the gain or loss of fat as well 
as of protein by the schematic body. 

For this purpose we first compute the gain or loss of protein 
in the manner already described. Using Kohler's factor for pro- 
tein (p. 67), a gain of 16.67 grams of nitrogen is equivalent to a 
gain of 100 grams of protein. This 100 grams of protein will 
contain, according to Henneberg, 53 grams, or according to Kohler, 
52.6 grams of carbon. Any gain of carbon in excess of this amount 
must therefore be in the form of non-nitrogenous organic matter, 
while if less than this amount of carbon has been gained the non- 
nitrogenous matter of the body must have been drawn upon to 
supply the difference. The only non-nitrogenous organic substance 
assumed to be present in the schematic body, however, is fat, con- 
taining on the average 76.5 per cent, of carbon (p. 61). Neces- 

*For a direct comparison of results obtained upon the horse by the Zuntz 
and the Pettenkofer forms of apparatus, see Lehmann, Zuntz, & Hagemann, 
Landw. Jahrb., 23, 125. 



78 PRINCIPLES OF ANIMAL NUTRITION. 

sadly, then, on this assumption, each gram of carbon gained in 
excess of that stored in the form of protein will represent 1.3 grams 
of fat stored. 

Formation of Glycogen. — Granting the substantial accuracy of 
the computation of the gain or loss of protein, the only serious 
criticism to which the above method of computing the gain or loss 
of fat is subject is that it does not take account of the possible stor- 
age of carbon in other forms, and particularly as glycogen. In 
other words, it may be contended that the schematic body should 
be regarded as consisting of water, ash, fat, and carbohydrates. 
There is undoubtedly a certain degree of justification for this con- 
tention, and the significance of small gains of carbon, or of gains 
observed during short periods, is by no means unambiguous. But 
when such a gain is observed to continue day after day for weeks 
on an unchanged ration, as in some of the experiments cited on 
subsequent pages, the objection loses all force. 

Computation of Total Metabolism. — The same principle 
may be applied to the computation of the total amount of protein 
and fat metabolized. From the urinary nitrogen (plus that of the 
feces if the latter be regarded as a metabolic product) by multipli- 
cation by the conventional factor we obtain, as already explained, 
the total proteid metabolism. Subtracting the amount of carbon 
corresponding to this quantity of protein from the total carbon 
excretion leaves a remainder which must have been derived from 
non-nitrogenous material. If carbohydrates are absent from the 
food, this material, in an experiment of any length, must be 
substantially fat, and the amount of the latter can be computed 
from the carbon by the use of the factor 1.3. In the presence of 
any considerable amount of carbohydrates, however, the results 
are ambiguous unless we know also the quantity of oxygen con- 
sumed. 

Other Determinations. — The great majority of investigations 
upon the metabolism of matter have been confined to determi- 
nations of the nitrogen and carbon balance. Occasionally, how- 
ever, other determinations have been made. 

Hydrogen Balance. — Determinations of water and of hydrogen 
in organic combination in food and excreta enable us, after making 



METHODS OF INVESTIGATION. 79 

allowances for the hydrogen gained or lost in protein and fat, to 
compute the gain or loss of water by the body. 

With the earlier forms of respiration apparatus, great diffi- 
culty was experienced in obtaining satisfactory results for the 
water,* and Stohmann f has traced the difficulty to an invisible 
condensation of water on the walls of the chamber and connections. 
More recently Rubner % has been able to make satisfactory deter- 
minations of water with a Pettenkofer apparatus by avoiding as 
much as possible differences of temperature between different parts 
of the apparatus and by taking the sample of the outcoming air for 
analysis as close to the respiration chamber as possible. Atwater 
& Rosa have shown that their form of Pettenkofer apparatus 
(p. 72) permits of very accurate determinations of water. 

Oxygen Balance. — Owing to the technical difficulties already 
indicated in considering the different types of respiration apparatus, 
direct determinations of the oxygen balance have rarely been made. 
This is the more to be regretted since such a determination would 
v erve to check those of nitrogen, carbon, and hydrogen, and would 
be a test of the accuracy of our deductions from those determina- 
tions as to the nature of the material gained or lost by the body. 

Ash Ingredients. — The gain or loss of ash ingredients can of 
course be readily determined, but the subject as yet has hardly 
received the attention which it deserves. 

Sulphur and PHOsPHORUS.^Sulphur forms an essential con- 
stituent of the proteids, while phosphorus enters into the composi- 
tion of the nucleins and also of lecithin. The determination of the 
income and outgo of these two elements is often of value in rela- 
tion to special physiological questions, but from the somewhat 
general standpoint of this work may be considered as of rather 
minor importance. 

*Zeit. f. Biol., 11, 126. 
-j-Landw. Vers. Stat., 19, 81. 
JArch. f. Hygiene, 11, 160. 



CHAPTER IV. 
THE FASTING METABOLISM. 

The matter which the animal organism derives from its food is 
applied substantially in three general directions : first, to the main- 
tenance of those vital activities, such as circulation, respiration, 
secretion, the metabolic activity of the various tissues, etc., and 
probably to some extent the direct production of heat, which in 
their entirety make up the physical life of the organism; second, 
to the support of those functions by which the crude materials 
ingested are prepared to nourish the body, that is, to the work of 
digestion and assimilation; third, to the production of external 
mechanical work or to the storage of surplus material in the form 
of growth of tissue. 

Of these three general functions of the food, the one first named 
is obviously of fundamental significance, and a determination of 
the nature and amount of its demands constitutes the natural first 
step in a study of the laws of nutrition. For this purpose we can 
eliminate the influence of the other two factors by keeping the ani- 
mal as nearly as possible in a state of absolute rest and by with- 
holding food. Under these circumstances the expenditure of matter 
from the tissues of the body may be taken as representing the 
miminum demands of the vital functions. It will therefore be both 
logical and convenient to consider first, in the present chapter, the 
fasting metabolism of the quiescent animal, while in succeeding chap- 
ters we take up the influence respectively of the food-supply and of 
external work upon metabolism. The protein of the food has such 
peculiar and distinct functions in the animal economy that it will 
be a matter of practical convenience to follow the historical order 
of investigation and consider first the proteid metabolism by itself 

80 



THE FASTING METABOLISM. 



81 



and subsequently the total metabolism as shown by the combined 
nitrogen and carbon balance. 

§ i. The Proteid Metabolism. 

Tends to Become Constant. — When food is withheld from a 
well-nourished animal, particularly a carnivorous animal, the proteid 
metabolism usually diminishes, at first rapidly and more slowly later, 
until within a few days it reaches a minimum value which may then 
remain nearly unchanged for a considerable time. This was first 
shown by the investigations of Carl Voit, in conjunction with 
Bischoff and later with v. Pettenkofer, and has been fully confirmed 
by later results. 

The following table shows the results obtained by Voit * in 
several experiments upon a dog weighing about 35 kgs., the pro- 
teid metabolism being expressed in grams of urea per day. As 
noted in Chapter III, such results are not absolutely accurate and do 
not represent the total proteid metabolism, but the fact that they 
are comparable is sufficient for our present purpose. 







Previous Food per Day. 




2500 Grms. 
Meat. 


1800 Grms. 

Meat; 

250 Grms. 

Fat. 


1500 Grms. 
Meat. 


1500 Grms. 
Meat. 


Nothing. 


Urea per da\ 
Last day o 
1st " ' 
2d " ' 
3d " ' 
4th " ' 
5th " « 
6th " ' 
7th " ' 
8th " ' 


f' 

f feeding .... 

t a 
t tt 

t it 
t a 

i a 


Grms. 

180.8 
60.1 
24.9 
19.1 
17.3 
12.3 
13.3 
12.5 
10.1 


Grms. 

130.0 
37.5 
23.3 

16.7 
14.8 
12.6 
12.8 
12.0 


Grms. 

110.8 
29.7 
18.2 
17.5 
14.9 
14.2 
13.0 
12.1 
12.9 


Grms. 

110.8 
26.5 
18.6 
15.7 
14.9 
14.8 
12.8 
12.9 
12.1 
11.9 
11.4 


Grms. 
24.7 
19.6 
15.6 
14.9 
13.2 
12.7 
13.0 


9th " ' 






10th " ' 


i a 























Two Factors of Proteid Metabolism. — In these, as in many 
similar experiments, the proteid metabolism was quite unequal on 
the last day of the feeding and on the first fasting day, but in a 



*Zeit. f. Biol., 2, 811. 



82 



PRINCIPLES OF ANIMAL NUTRITION. 



comparatively short time it sank to a minimum which was practi- 
cally the same in all the experiments upon this particular animal, 
viz., the equivalent of about 12 grams of urea per day. This mini- 
mum we may fairly regard as representing the necessary and inev- 
itable destruction of proteids involved in the vital processes of 
the organism, and therefore may consider as taking place also 
when the animal was fed. If, now, we subtract from the total 
urea excreted the 12 grams corresponding to the minimum de- 
mand of the body, there is revealed the second and variable factor 
of the proteid metabolism, which is large in the well-fed animal but 
rapidly disappears during fasting, as the following table shows: 







Previous Food per Day. 






1800 Grms. 












2500 Grms. 


Meat and 


1500 Grms. 


1500 Grms. 


Nothing. 






Meat. 


250 Grms. 


Meat. 


Meat. 








Fat. 








Urea per day: 


Grms. 


Grms. 


Grms. 


Grms. 


Grms. 


Last day 


Df feeding 


168.8 


118.0 


98.8 


98.8 


12.7 


1st " 


' fasting 


48.1 


25.5 


17.7 


14.5 


7.6 


2d " 


« it 


12.9 


11.3 


6.2 


6.6 


3.6 


3d " 


i a 


7.1 


4.7 


5.5 


3.7 


2.9 


4th " 


i <t 


5.3 


2.8 


2.9 


2.9 


1.2 


5th " 


i n 


0.3 


0.6 


2.2 


2.8 


0.7 


6th " 


t It 


1.3 


0.8 


1.0 


0.8 


1.0 


7th " 


I It 


0.5 


0.0 


0.1 


0.9 




8th " 


I It 


-1.9 




0.9 


0.1 




9th " 


I It 








-0.1 
-0.6 




10th " 


I It 























Organized and Circulatory Protein. — It is evident from 
the above results, and will appear still more clearly when we come 
to consider the influence of the food-supply upon proteid meta- 
bolism, that in addition to the great mass of proteid tissue in the 
body, whose metabolism results in the excretion of a relatively 
small and constant amount of nitrogenous products, the well- 
nourished organism may also contain variable amounts of nitrogen- 
ous matter which is subject to rapid metabolism and which speed- 
ily disappears during fasting. Voit employed the term circula- 
tory protein (Zirkulationseiweiss) to designate this variable store 
of rapidly metabolized nitrogenous matter, which he regards as 
being substantially the dissolved protein which penetrates from 



THE FASTING METABOLISM. 83 

the blood and lymph into the cells of the tissues, while he termed 
the protein of the organized tissues, which is relatively stable and 
but slowly metabolized, organized protein (Organeiweiss) . The 
amount of the circulatory protein is small in all cases as compared 
with that of the organized protein, its absolute amount being de- 
pendent, as the above tables indicate and as will appear more 
clearly in the next chapter, upon the supply of proteids in the 
food. Owing to its rapid metabolism, however, it furnishes by 
far the larger part of the nitrogenous waste products in the liberally 
fed animal. 

That the anatomical distinctions implied in the terms used by 
Voit correspond to the actual facts of the case has been disputed 
and may be open to question, but for our present purpose this does 
not particularly concern us. The fact of the existence of the two 
factors of proteid metabolism, viz., a variable one, depending upon 
the previous food-supply and a relatively constant one independ- 
ent of the latter is fully established, by whatever names we may 
choose to call them. 

A Minimum of Protein Indispensable. — While the proteid 
metabolism of the fasting animal is speedily reduced to relatively 
small proportions, it is never entirely suspended as long as the 
animal lives. Moreover, to anticipate a portion of the follow- 
ing chapter, even the most liberal supply of non-nitrogenous 
nutrients is powerless to suspend or very greatly reduce the pro- 
teid metabolism of a fasting animal. A certain amount of proteid 
metabolism is indissolubly associated with the continuance of life, 
and neither the fat of the body nor the non-nitrogenous ingredients 
supplied in the food can perform these special functions of protein 
in the body. 

§ 2. Total Metabolism. 

Constant Loss of Tissue. — Common observation, no less than 
scientific investigation, teaches that a fasting animal suffers a con- 
tinual loss of tissue. Such an animal derives the energy required 
for its vital activities from the metabolism of its store of proteids 
and of fat. As regards the former, we have just seen that in a 
short time, or as soon as the influence of the previous supply of 



8 4 



PRINCIPLES OF ANIMAL NUTRITION. 



proteids in the food is exhausted, the proteid metabolism reaches 
a minimum and thereafter remains nearly constant for a consider- 
able time, and subsequent investigations have shown that this 
constancy is still more marked when the proteid metabolism is 
computed per unit of live weight. 

What has thus been found to be true of the proteid metabolism 
has also been shown to hold good of the total metabolism of pro- 
teids plus body fat. As soon as the influence of the previous food 
has disappeared, the rate of metabolism of both proteids and fat 
shows but slight variations throughout a considerable time. Of 
the early experiments of Pettenkofer and Voit, the following * may 
be cited as illustrating approximately this constancy: 





Series a, 1862. 


Series b, 1861. 




March 10, 
6th Day. 


March 14, 
10th Day. 


April 5, 
2d Day. 


April 8, 
5th Day. 


April 11, 
8th Day. 


Live weight 


Kgs. 
31.21 

Grms. 
104.1 
5.95 

37.18 
107. 

1.19 
3.43 


Kgs. 
30.05 

Grms. 
82.4 
5.23 

32.69 
83. 

1.09 

2.76 


Kgs. 
32.87 

Grms. 

108.7 

11.6 

72.51 

86. 

2.21 
2.62 


Kgs. 
31.67 

Grms. 

100.0 

5.7 

35.63 
103. 

1.13 
3.25 


Kgs. 

30.54 


Total loss: 
Proteids 


Grms. 

93.2 

4.7 

29.38 


Fat 


99.2 


Loss per Kg. live weight: 
Proteids 


0.96 


Fat 


3.25 







Finkeler f determined the respiratory exchange of fasting 
guinea-pigs in two-hour periods. Upon the highly probable assump- 
tion that their proteid metabolism was relatively small and con- 
stant, the results of such experiments would furnish a measure of 
the relative intensity of the total metabolism. Finkeler 's average 
results are contained in the table on the opposite page. 

But a slight decrease in the amount of oxygen consumed is 
observed in the different stages of the fasting, while there is a 
marked decrease in the amount of carbon dioxide produced. The 
relation between these two quantities, as expressed by the respira- 
tory quotient,! shows us that at the beginning of the fasting the 
metabolism was largely at the expense of the carbohydrates of the 
* Zeit. f. Biol., 5, 369. f Arch. ges. Physiol., 23, 175. \ Compare p. 74. 



THE FASTING METABOLISM. 



85 





Per Hour and Kg. Live Weight. 




Length of Fasting, 
Minutes. 


Oxygen Consumed, 
c.c. 


Carbon Dioxide 

Excreted, 

c.c. 


Respiratory- 
Quotient. 



1468 
2950 


1202.19 
1154.53 
.1146.76 


1111.80 
923.75 
811.12 


0.93 
0.80 
0.71 



1575 
3543 
5940 


1250.28 
1226.18 
1241.78 
1192.50 






334 
1712 
3233 


1959.45 
1850.02 
1809.85 


1494.68 
1318.19 
1289.63 


0.76 
0.71 
0.71 



body, while as the experiment progressed the store of carbohydrates 
(glycogen) in the body was gradually exhausted and the meta- 
bolism finally became a fat metabolism. Since, now, as will be 
shown in Chapter VIII, the consumption of equal amounts of oxygen 
results in the liberation of approximately equal amounts of energy 
whether that oxygen is employed to oxidize carbohydrates or fats, 
Finkeler concludes that the total metabolism, as measured in terms 
of energy, was nearly constant. 

Lehmann and Zuntz * have observed a similar constancy of 
the respiratory exchange per unit of weight in the case of two 
men fasting for eleven and six days respectively, while Munk f 
found their urinary nitrogen to be also approximately constant. 
Magnus-Levy J has likewise observed a similar constancy in the 
respiratory exchange of the dog and of man during fasting, as have 
also Johansson, Landgren, Sonden, & Tigerstedt § for man. 

RubnerJ as a preliminary to his investigations upon the re- 
placement values of the nutrients, discusses this question at some 
length and gives the results of experiments upon dogs, rabbits, 
guinea-pigs and fowls, in which the excretion of nitrogen and car- 
bon per unit weight shows a marked degree of constancy through 
considerable periods. 

* Virchow's Archiv, 131, Supp. % Arch. ges. Physiol., 55, 1. 

■\Ibid. §Skand. Archiv. f. Physiol., 7, 29. 

|| Zeit. f. Biol., 17, 214; 19, 313; Biologische Gesetze, p. 15. 



86 PRINCIPLES OF ANIMAL NUTRITION. 

Metabolism Proportional to Active Tissue. — In a critical 
discussion of these and other results on fasting animals, to which 
we shall have occasion to refer again in Part II, E. Voit * shows 
that a still more constant relation is obtained when either the pro- 
teid or the total metabolism is compared with the total mass of 
proteid tissue estimated to be contained in the body on the several 
days of the experiment. The total protein of the body, however, 
may be regarded as at least an approximate measure of the active 
cell mass, as distinguished from the relatively inactive cells of 
adipose tissue. It is the vital activities of the former, in the fast- 
ing animal, that mainly determine the amount of the total meta- 
bolism, the energy liberated being supplied in part by the relatively 
small amount of proteid metabolism which goes on in the cells of 
the fasting animal, but largely by the metabolism of fat supplied 
to the active cells from the adipose tissue. 

Ratio of Proteid to Total Metabolism. — In the preceding 
paragraph it was implied that the proteid metabolism constitutes 
but a small portion of the total metabolism of the fasting animal, 
the remainder of the necessary energy being supplied, after the 
small store of glycogen in the body is exhausted, by the metabo- 
lism of body fat. Rubner f appears to have been the first to call 
specific attention to this aspect of the question. In his investiga- 
tions upon the relation of size of animal to total metabolism he 
adduces experimental results to prove that this ratio is not mate- 
rially different in large and in small animals. The question has, 
however, been more recently discussed by E. Voit J from a general 
point of view, the results of numerous investigators being summa- 
rized. In discussing these results, Voit has computed from the 
nitrogen and carbon balance, when these data were available, in 
substantially the manner described in Chapter VIII, the amount of 
energy liberated by the metabolism of the protein and fat lost by 
the body. In those instances in which only the nitrogen balance 
was determined, he estimates the amount of energy liberated in 
the body from the computed surface on the basis of average results 
with similar animals. (Compare Chapter XI, § 2.) Taking this 
amount, expressed in calories, as the measure of the total meta- 
bolism, and including only experiments in which the animals 
* * Zeit. f. Biol., 41, 113. t Ibid., 19, 557. \ Ibid., 41, 167. 



THE FASTING METABOLISM. 



87 



are believed to have been in good bodily condition (well nourished) 
at the beginning of the trials, he obtains the following average 
results : 





Live Weight, 
Kgs. 


Nitrogen Excretion per Day. 


Proteid 




Total, 
Grms. 


Per Kg. 

Live Weight, 

Grms. 


Metabolism 
in % of Total 
Metabolism. 


Swine 


115.0 

63.7 

(28.6 

\ 18.7 

( 7.2 

2.7 

0.6 

3.3 

2.1 


6.8 
12.6 
5.1 
3.8 
2.2 
1.2 
0.4 
0.8 
0.7 


0.06 
0.20 
0.18 
0.20 
0.30 
0.46 
0.65 
0.23 
0.34 


7 3 


Man 


15 6 


Dog 


13.2 

10 7 


Rabbit 


13.5 
16 5 


Guinea pig 

Goose 

Hen 


10.8 

7.4 

10 







As will appear later, the total metabolism of a small animal is 
greater per unit of weight than that of a large animal. The above 
figures show that the same thing is true of the proteid metabolism. 
When, however, the proteid metabolism is computed as a percent- 
age of the total metabolism, as in the last column of the table, this 
dependence upon the live weight disappears. While the figures 
still show considerable variations, these are much reduced and 
show no connection with the live weight. In other words, the proteid 
metabolism tends to be a somewhat uniform percentage of the 
total metabolism, ranging in these experiments, aside from two 
apparently exceptional results, between 10 and 16 per cent. 

The individual experiments cited by Voit show a similar general 
uniformity, both in the same animal on successive days of fasting 
and in case of different animals. Thus twenty-seven experiments 
on the dog gave the following : 



Range of Proteid Metabolism in Per Cent. 


Number of Cases. 


of Total Metabolism. 


Absolute. 


Per Cent. 


Less than 10 


4 

15 

5 

3 

27 


14.8 


10-14 


55.6 


14-17 


18.5 


More than 17 


11.1 








100.0 



88 PRINCIPLES OF ANIMAL NUTRITION. 

The great majority of cases gave values lying between 10 and 
17 per cent. 

Effect of Body Fat. — Both from the summary on p. 87 and 
from the individual results cited by Voit, it is evident that while 
the proportion of energy supplied by the metabolism of pro- 
teids in the fasting animal is normally small and varies only within 
rather narrow limits, it is still subject to relatively considerable 
variations. The most important cause of these variations in the 
fasting animal under uniform external conditions appears to be 
the ratio of fat to protein in the body. 

C. Voit * appears to have first noted that when fasting is pro- 
longed sufficiently to nearly exhaust the reserve of visible fat in 
the body, the proteid metabolism, after remaining nearly constant 
or decreasing slightly for some days, as in the examples just given, 
begins to increase somewhat rapidly. This increase Voit attrib- 
uted to the exhaustion of the fat, the oxidation of which had hith- 
erto partially protected the organized proteids of the body. Sub- 
sequent investigations, particularly Rubner's,f have in general 
confirmed Voit's observation, while giving it a somewhat more 
general form. 

E. Voit X has recently reviewed the available experiments upon 
fasting metabolism in their bearing on this question. From the 
experimental data he computes or estimates, first the ratio of pro- 
teid to total metabolism (expressed in terms of energy), and second 
the ratio of proteids to fat in the body on the several days of each 
experiment. A comparison of these ratios shows a very marked 
correspondence, a high ratio of proteids to fat in the body coin- 
ciding with a large proteid metabolism compared with that of fat, 
and vice versa. The graphic representations of the relations as 
given by Voit are especially convincing. Moreover, the results 
show that the extent of the proteid metabolism does not depend 
directly upon the duration of the fasting. With different animals, 
or with the same animal under different conditions, a certain ratio 
of proteid to total metabolism is attained whenever the correspond- 
ing ratio of proteid tissue to fat in the body is reached, whether this 
be early or late in the experiment. 

The growing ratio of proteid to total metabolism in the fasting 
* Zeit. f. Biol., 2, 326. f Loc. cit. See p. 86. % Zeit. f. Biol., 41, 502. 



THE FASTING METABOLISM. 89 

animal is explained by Voit to be due to an increasing difficulty in 
transferring the reserve fat from the adipose tissues, thus resulting 
in a diminution of the amount of fat (or its cleavage products?) 
circulating in the organism. If the body is well supplied with fat 
at the outset this phenomenon does not at first appear, and the 
ratio of proteid to total metabolism remains nearly constant for a 
time. . 

With continued fasting the store of body fat is, as has just been 
shown, drawn upon much more rapidly than that of protein, while 
at the same time the total amount of the former present at the 
beginning of fasting is often less than that of the latter. As a 
necessary result, the ratio of fat to protein in the body decreases. 
When this decrease passes a certain point, the fat of the adipose 
tissue is drawn upon with more and more difficulty for material to 
supply the demand for energy, and as a result additional protein is 
metabolized to make good the deficiency of available fat. From 
this time on, the ratio of proteid to total metabolism shows a con- 
tinually accelerated increase. The time when the increase in the 
proteid metabolism becomes marked depends upon the original 
condition of the body. If the animal is well nourished, and espe- 
cially if it contains large reserves of fat, the increase may be long 
deferred or even fail to appear at all. If, on the other hand, it is 
poorly nourished and contains little fat, an increase of the proteid 
metabolism may take place almost from the outset. The following 
three examples, cited by E. Voit from Rubner's experiments, may 
serve to illustrate these three types of fasting metabolism: 



Guinea Pig. 


Dog. 


Rabbit. 


Day of 
Fasting. 


Proteid 
Metabolism 
in % of Total 
Metabolism. 


Day of 

Fasting. 


Proteid 
Metabolism 
in % of Total 
Metabolism. 


Day of 
Fasting. 


Proteid 
Metabolism 
in % of Total 
Metabolism. 


2 

3 

4 

5 

6 

7 

8 

9 


10.4 
11.1 
11.0 

11.9 
11.8 
6.9 
11.2 
10.9 


2-4 
10-11 
12 
13 
14 


16.3 
13.1 
15.5 
17.4 
20.0 


3 

5-7 

9-12 

13-15 

16 

17-18 


16.5 
23.6 
26.5 
29.8 
50.1 
96.4 



90 PRINCIPLES OF ANIMAL NUTRITION. 

Schulze * claims that this increase in the proteicl metabolism of 
the fasting animal is not, in all cases at least, due to lack of fat or 
other non-nitrogenous material to protect the protein from destruc- 
tion. He advances the hypothesis that the loss of protein incident 
to the fasting so injures the cells that finally many of them die 
and the protein of their protoplasm becomes part of the circula- 
tory protein of the body and is rapidly decomposed, thus giving 
rise to an increased excretion of nitrogen. 

While it is not impossible that this ingenious hypothesis has 
some basis of fact, Kaufmann,f in a quite full review of the litera- 
ture of the subject, together with original experiments, shows 
that it can by no means supplant Voit's explanation. He points 
out in particular that the time when the increase in the proteid 
metabolism begins seems to bear no relation to the loss of protein 
which the body has sustained, while, on the other hand, it coin- 
cides quite closely with the time when the supply of visible fat is 
nearly exhausted. % 

Summary. — In the light of the facts set forth in the foregoing 
paragraphs we may sketch the general outlines of the fasting meta- 
bolism somewhat as follows: 

In the early stages of fasting, particularly if the previous food 
has contained an abundance of proteids, the proteid metabolism 
may be considerable. As the effect of the previous food disappears, 
however, and the store of " circulatory protein " in the body is ex- 
hausted, the proteid metabolism speedily falls to the minimum 
amount required for the vital activities of the protoplasm, and the 
remaining demands of the body for energy are supplied by the 
metabolism of the stored-up fat. If the latter is fairly abundant, 
this stage may last several days, the total metabolism remaining 
nearly constant and the proteids supplying a nearly constant pro- 
portion of the necessary energy (according to E. Voit about 15-16 
per cent.)." Sooner or later, however (unless in a very fat animal), 
the supply of fat from the adipose tissue begins to flag. The de- 
mand for energy, however, remains unabated, and as the fat-supply 
falls off, more and more protein is metabolized in its place, until at 

* Arch. ges. Physiol., 76, 379. f Zeit. f. Biol., 41, 75. 

^Compare also E. Voit's critique of Schulze's investigations. (Zeit. f. 
Biol., 41, 550.) 



THE FASTING METABOLISM. 91 

last the metabolism may even become almost entirely proteid in 
its character. We have in these facts the first of the numerous 
illustrations which we shall meet in the course of this discussion 
of the plasticity of the organism in adapting itself to differences 
in the food-supply, and of the controlling influence exerted upon 
the course of its metabolism by the demand for energy. 

The Intermediary Metabolism. — The prime object of the 
metabolism of the quiescent fasting animal is, as already pointed 
out, to supply energy for the performance of the vital functions. 

Mention has already been made in Chapter II of the hypothesis 
that the immediate source of energy to the cells of both muscles 
and glands is the metabolism of carbohydrate material. This 
hypothesis in effect regards the metabolism of the fasting animal as 
divisible into three processes : first, the splitting up of the proteids, 
yielding urea and fat; second, the partial oxidation of fat, whether 
derived from the proteids or from the adipose tissue, yielding dex- 
trose; third, the oxidation of the resulting dextrose in the tissues. 

So far as the kind and amount of excretory products are con- 
cerned, it of course makes no difference whether the metabolism 
takes place in accordance with this hypothesis or whether the 
proteids and fat are oxidized directly in the tissues. In either 
case the fasting animal lives upon its store of proteids and fat, and 
the resulting excretory products, as well as the amount of heat 
produced, are qualitatively and quantitatively the same, so that 
the coincidence observed by Kaufmann * between the observed 
results and those computed from his equations is without special 
significance in this case. 

There is, nevertheless, an important and essential difference in 
the two views. If we regard the proteids and fat as yielding up 
their energy directly for the vital activities, then all the energy 
thus liberated is available for this purpose. If, on the contrary, 
we suppose these substances to be first partially metabolized in the 
liver or elsewhere in the organism, then only that portion of their 
potential energy which is contained in the resulting dextrose is 
available directly for the general purposes of the body. The re- 
mainder of their energy is liberated as heat during the preliminary 
* Archives de Physiologie, 1896, pp. 329 and 352. 



92 PRINCIPLES OF ANIMAL NUTRITION. 

metabolism, and while contributing its quota towards maintaining 
the normal temperature of the body is not directly available for 
other purposes. In other words, the question is not one as to the 
total energy liberated, but as to its form and distribution. As 
regards the fasting animal itself, the question is of minor impor- 
tance; but, as will appear in subsequent chapters, it materially 
affects our views as to the relative values of the several nutrients 
of the food. 



CHAPTER V. 
THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 

The metabolism of the fasting animal was regarded in the pre- 
ceding chapter as representing the essential demands of the vital 
functions for a supply of matter as a vehicle of potential energy. 
Under these conditions, as we have seen, the total metabolism bears 
a close relation to the mass of active tissue, while the qualitative 
character of the metabolism, that is the ratio of proteid to non- 
proteid matter consumed, appears to be likewise constant for any 
given condition of the body, depending upon the relative supply 
of proteids and non-nitrogenous matters to the active cells. When 
food is given to such an animal the conditions are modified in essen- 
tially three ways: % 

First, to the metabolism incident to the fasting state is added 
that required to supply the energy consumed in the digestion and 
assimilation of the food. 

Second, the food-supply may alter the proportions in which the 
various nutrients are supplied to the active cells, and thus affect 
the metabolism qualitatively, giving rise to a relatively greater 
or less metabolism of proteids, fats, carbohydrates, etc. 

Third, the food-supply may be in excess of the requirements of 
the body and lead to a storage of matter of one sort or another. 

The quantitative relations of the food-supply to the total 
metabolism and to the storage of matter and energy in the body 
may be most satisfactorily considered upon the basis of the amounts 
of energy involved. Accordingly we may content ourselves here 
with a simple mention of this side of the question, deferring a dis- 
cussion of it to Part II and confining the present chapter largely 
to a study of the qualitative changes in the metabolism brought 
about by variations in the food-supply. As in the previous chapter, 
it will be convenient to consider the relations of the proteids of the 

93 



94 PRINCIPLES OF ANIMAL NUTRITION. 

food and of the body separately from those of the non-nitrogenous 
nutrients. 

§ i. The Proteid Supply. 

The effects of the proteid supply upon metabolism may be most 
readily and clearly traced in experiments in which the food consists 
solely, or nearly so, of proteids, deferring to the next section a 
consideration of the modifications introduced by the presence of 
non-nitrogenous nutrients' in the food. 

Effects on Proteid Metabolism. 

Our knowledge of the relations between proteid supply and 
proteid metabolism in the animal body is based upon the funda- 
mental investigations of Bischoff & Voit,* Carl Voit,f and Petten- 
kofer & Voit,f at Munich. The results of these researches have 
been so fully confirmed by subsequent investigators and have 
become so much the common property of science that it is unneces- 
sary to do more than summarize them here, with the addition of 
such examples as may seem best adapted to illustrate them. 

Amount Required to Reach Nitrogen Equilibrium. — As 
we have seen, the proteid metabolism of a fasting animal speedily 
reaches a minimum which we may probably regard as representing, 
at least approximately, the amount of proteids necessarily broken 
down and oxidized in the vital activities of the tissues of the body. 
If we supply proteid food to such an animal, we might naturally 
be inclined to expect that the first use to which the proteids of 
the food would be put would be to stop the loss of proteid tissue, 
and that if as much proteid was supplied in the food as was being 
metabolized in the body, nitrogen equilibrium would be reached. 

Experiment shows, however, that this is very far from being 
the case. Even the least amount of proteids causes a prompt 
increase in the urinary nitrogen, and each successive addition of 
proteids results in a further increase, so that it is not until the food 
proteids largely exceed the amount metabolized during fasting 
that nitrogen equilibrium is reached. Thus Bischoff & Voit, J 

* Gesetze der Ernahrung des Fleischfressers, 1860. 

t Published chiefly in the Annalen der Chemie und Pharmacie and the 
Zeitschrift fi'ir Biologie. See also Voit, "Physiologie des Stoffwechsels," in 
Herman's Handbuch der Physiologie. 

% Zeit. f. Biol., 3, 29 and 33. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 



95 



in a series of experiments upon a dog fed exclusively on lean meat, 
obtained the results shown in the following table, the proteid 
metabolism being expressed in terms of flesh with its normal water 
content (N X 29.4) instead of dry proteids: 



Date. 


Meat Fed. 


" Flesh " 
Metabolized. 


Gain or Loss 
of Flesh. 


1S58. 
Aug. 25 






300 

600 

900 

1200 

1500 


223 

190 
379 
665 
941 
1180 
1446 


-223 


" 26 


-190 


" 27 and 28 


- 79 


" 29-Sept. 1 


- 65 


Sept. 2 and 3 


- 41 


" 4 " 5 


+ 20 


" 6 " 7 


+ 54 



Nov. 16 


1800 

1500 

1200 

900 

600 

300 

176 




1764 

1510 

1234 

945 

682 
453 
368 
220 


+ 36 


" 17 and 18 


- 10 


" 18 " 19 


- 34 


" 20 " 21 


- 45 


" 22 " 23 


- S2 


" 24 " 25. . . . 


-153 


" 26 " 27 


-192 


" 28-Dec. 1 


-226 







A much later series by E. Voit & Korkunoff,* in which the 
results were determined in terms of nitrogen, may be cited to illus- 
trate the same point. The food was lean meat from which the 
extractives had been removed by treatment with cold water. It 
contained 1.25 to 1.96 per cent, of fat. 



Food. 




Nitrogen in 




Food, 
Grms. 


Feces and Urine , 
Grms. 


Gain or Loss, 
Grms. 


Nothing 



4.10 

5.74 

6.77 

7.59 

8.20 

10.24 

11.99 

15.58 

13.68 


3.996 

5.558 

6.495 

7.217 

7.804 

8.726 

10.579 

12.052 

14.314 

13.622 


-3.996 


100 grms. extracted meat 

140 " " " 


-1.458 
-0.755 


165 " " " 


- . 447 


185 " " " . 


-0 214 


200 " " " . 


-0.526 


230 " " " 


-0.339 


360 " " " 


-0.062 


410 " " 


+ 1.266 


460 " " " 


+ 0.058 







* Zeit. f. Biol., 32, 67. 



96 PRINCIPLES OF ANIMAL NUTRITION. 

The proteid supply gradually overtakes the proteid metabolism, 
but when only proteids are fed the supply must largely exceed the 
fasting metabolism in order to attain nitrogen equilibrium. E. 
Voit has endeavored to obtain a numerical expression for this 
relation by taking as the basis of comparison the fasting meta- 
bolism. He estimates (loc. cit., p. 101) that of the total nitro- 
gen excretion of a fasting animal 81.55 per cent, is derived from 
true proteids and 18.45 per cent, from the extractives of the 
muscles. Since the food in his experiments consisted substan- 
tially of true proteids, he compares its nitrogen with 81.55 per 
cent, of the nitrogen of the excreta and thus finds that the mini- 
mum supply of proteid nitrogen required to reach nitrogen equi- 
librium was between 3.67 and 4.18 times that metabolized during 
fasting, the true value being estimated at 3.68. Five other less 
exact experiments gave confirmatory results and similar confirma- 
tion is found in the experimental results of C. Voit. 

Effect of Excess of Proteids. — If the supply of proteids to 
a mature animal be still further increased after nitrogen equilib- 
rium is reached, the excess of proteids is promptly metabolized, 
its nitrogen reappearing in the excreta. In other words, the ex- 
cretory nitrogen keeps pace with the supply of nitrogen in the food. 
The experiments by Bischoff & Voit just cited serve to illustrate 
this fact also. Approximate nitrogen equilibrium was reached on 
1200-1500 grams of meat, but in other trials even double this 
supply caused but a slight apparent gain of nitrogen, and it is 
probable that if the total urinary nitrogen had been determined 
instead of the urea, and account taken of the nitrogen of the 
feces, even this small difference would have disappeared. 

It is needless to multiply examples of this perfectly well-estab- 
lished fact. The animal body puts itself very promptly into equi- 
librium with its nitrogen supply and no considerable or long-con- 
tinued gain of proteid tissue can be produced in the mature animal 
by even the most liberal supply of proteid food. 

Transitory Storage of Proteids. — But while no continued 
gain of protein by the body can be brought about by additions to 
the proteid food, nevertheless, during the first few days following 
such an increase in the proteid supply a transitory storage of nitro- 
gen takes place. Conversely, too, a decrease in the proteid supply 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 



97 



causes at first a loss of nitrogen from the body, which, however, 
unless the new supply of proteids falls below a certain minimum is 
as transitory as the gain in the other case. In other words, while 
the nitrogen excretion of the mature animal is in the long run 
equal to the supply in the food, when the amount of the latter 
is changed the full effect on the excretion is not realized at once. 
This fact is well illustrated by the following selection from 
C. Voit's investigations upon the dog,* the results being expressed 
in terms of " flesh " : 





New 


" Flesh " Metabolized per Day. 


Previous 








Ration. 


Ration. 
Grms. 


On 
Previous 






Grms. 
















Meat. 


Meat. 


Ration. 


1st Day. 


2d Day. 


3d Day. 


4th Day. 


5th Day. 


6th Day. 


7th Day. 






Grms. 


Grms. 


Grms. 


Grms. 


Grms. 


Grms. 


Grms. 


Grms. 


1800 


2500 


1800 


2153 


2480 


2532 










500 


1500 


547 


1222 


1310 


1390 


1410 


1440 


1450 


1500 





1500 


176 


1267 


1393 


1404 










2500 


2000 


2500 


2229 


1970 












1500 


1000 


1500 


1153 


1086 


1088 


1080 


1027 






1000 


5000 


1000 


706 


610 


623 


560 









An example of the same fact is found in the experiments cited 
on p. 81, in which &\. proteid food was withdrawn, the nitrogen 
excretion falling rapidly, but reaching its minimum only after three 
or four days. 

Voit explained the facts just adduced as the consequence of 
the difference between organized and circulatory proteids already 
noted on p. 82. According to this hypothesis, the amount of 
the proteid metabolism is chiefly determined by the store of circu- 
latory proteids in the body. The ingestion of additional proteids 
increases the amount of these circulatory proteids in the body, and 
as a consequence the proteid metabolism increases until the nitrogen 
excretion overtakes the supply. Similarly, a decrease in the pro- 
teid food has the converse effect. 

Proteid Metabolism and Nitrogen Excretion. — Up to this 
point, following common usage, the terms nitrogen excretion and 
proteid metabolism have been employed as practically synony- 
mous. In one sense this usage is correct, but it is liable to give 
* E. v. Wolff, Emahrung Landw. Nutzthiere, p 271. 



98 PRINCIPLES OF ANIMAL NUTRITION. 

rise to a misconception. It is perfectly true that the presence of 
one gram, e.g., of nitrogen in the urine, implies that about six grams 
of protein have yielded up their nitrogen in the form of urea or 
other metabolic products and therefore have ceased to exist as pro- 
tein. It by no means follows from this, however, that this protein 
has been completely oxidized to carbon dioxide and water. We 
have already seen (Chapter II, p. 48) that the abstraction of the 
elements of urea from protein leaves a non-nitrogenous residue 
equal to nearly two-thirds of the protein, and that there is reason 
to believe that this residue may, according to circumstances, be 
oxidized to supply energy or give rise to a production of glycogen 
or of fat. In other words, the separation of its nitrogen from pro- 
tein and the complete oxidation of its carbon and hydrogen are 
two distinct things. When, therefore, we assert, on the basis of 
the evidence noted above, that the proteid metabolism of the mature 
animal is determined by the supply of proteids in the food, what 
we really mean is that the cleavage of proteids and the excretion 
of their nitrogen is so determined. 

Rate of Nitrogen Excretion. — A consideration of the course 
of the nitrogen excretion after a meal of proteids is calculated to 
throw light upon the relations of nitrogen cleavage to the total 
metabolism of the proteids. The early investigations of Becher, 
Voit, Panum, Forster, and Falck showed that when proteids are 
given to a fasting animal the rate of nitrogen excretion shows a 
rapid increase, reaching a maximum within a few hours. 

Feder * observed the maximum rate of nitrogen excretion by 
dogs in different experiments between the fifth and eighth hour 
after a meal of meat. From this point the rate of excretion de- 
creased less rapidly than it had increased and continued to decrease 
until about thirty-six hours after the meal. 

Graff enberger,f experimenting upon himself, obtained similar 
results after the consumption of fibrin, gelatin, and asparagin, while 
the results with a commercial "meat peptone" were markedly 
different; and Rosemann.J in studies upon the rate of nitrogen 
excretion by man, traces clearly a similar influence of the ingestion 
of nitrogenous food, while Krummacher's § results on dogs fully 

* Zeit. f. Biol., 17, 531 ; Thier Chem. Ber., 12, 402. t Zeit. f. Biol., 28, 318. 
t Arch. ges. Physiol., 65, 343. § Zeit. f. Biol., 35, 481. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 



99 



confirm those of Feeler. Sherman and Hawk * have likewise found 
the curve of nitrogen excretion by man after the ingestion of lean 
meat to show the same general form observed by Feder and by Graf- 
fenberger. 

Nitrogen Cleavage Independent of Total Metabolism. — 
Kaufmann,f by the method outlined in Chapter VIII, has made 
a series of determinations of the nitrogen excretion, respiratory 
exchange, and heat production of dogs during the time when nitro- 
gen cleavage is most active, i.e., from the second to the seventh hour 
after a full meal of meat. From his theoretical equations for the 
complete metabolism of proteids (pp. 51 & 75) he computes the 
respiratory exchange and heat production corresponding to the 
observed excretion of urinary nitrogen and compares them with 
the actual results per hour as follows: 





Proteid 
Meta- 

bolism.J 
Grms. 


Computed. 


Observed. 




CO a 

Excreted. 

Liters. 


o a 

Consumed. 
Liters. 


Heat Pro- 

duction. 

Cals. 


CO, 

jExcreted. 

Liters. 


0, 

Consumed. 

Liters. 


Heat Pro- 
duction. 

Cals. 


No. 1... 


9.329 


8.132 


9.745 


45.0 


5.953 


6.767 


30.6 


" 2... 


9.926 


8.565 


10.373 


48.0 


7.064 


7.972 


34.6 


" 3... 


9.350 


8.153 


9.771 


45.4 


7.161 


8.236 


34.0 


" 4... 


9.540 


8.231 


9.864 


45.8 


7.398 


8.673 


34.0 


" 5... 


6.632 


5.783 


6.930 


32.0 


5.228 


6.596 


27.7 


" 6... 


9.491 


8.276 


9.918 


46.1 


6.393 


7.813 


29.7 


" 7... 


8.685 


7.573 


9.075 


42.2 


6.325 


7.730 


29.0 


" 8... 


9.958 


8.683 


10.406 


48.4 


6.702 


7.903 


33.6 


" 9... 


8.928 


7.785 


9.235 


43.0 


6.062 


7.916 


35.3 


" 10... 


10.553 


9.202 


11.027 


51.0 


7.125 


8.589 


32.7 



But a glance is needed to show that the total metabolism, 
whether measured by the gaseous exchange or by the heat produc- 
tion, is much less than that computed, which is equivalent to saying 
that the non-nitrogenous residue of the proteids was not completely 
oxidized. Gruber,§ whose experimental results upon the rate of 
nitrogen excretion fully confirm those above cited, has shown very 
clearly the bearing of these facts. He points out that if we 

* Amer. Jour. Physiol., 4, 25. 
f Archives de Physiologic, 1896, pp. 346 and 768. 

\ Kaufmann's factor for proteids, derived from the formula C 72 H 112 Nj 8 2 ,S f 
is 6.39. 

§ Zeit. f. Biol., 42, 407. 

L.ofC. 



ioo PRINCIPLES OF ANIMAL NUTRITION. 

regard the nitrogen excretion as denoting the complete metabo- 
lism to carbon dioxide, water, urea, etc., of a corresponding 
amount of proteids, we get figures for the total evolution of 
energy (heat) in the organism which are entirely incompatible 
with those derived from other considerations. For example, a 
daily diet of 1500 grams of lean meat given to a dog not only suf- 
ficed to supply the demands for energy but produced a storage of fat 
in the body. The total daily production of heat, computed from 
the results of respiration experiments (see Chapter VIII), was 
1060.2 Cals., equivalent to 88.3 Cals. in two hours, which must have 
been derived essentially from the metabolism of proteids. If, how- 
ever, we compute the evolution of energy from the results of the 
nitrogen excretion as determined in two-hour periods, we get strik- 
ingly variable results. 



Hour. 


Urinary Nitrogen, 
Grams. 


Equivalent Energy,* 
Cals. 


9 11 


3.11 
5.71 

6.62 
6.98 
6.35 
6.04 
5.08 
2.65 
1.24 


80.6 


11 1 


148.2 


13 


171.6 


3 5 


181.2 


5 7 


165.1 


7 9 


156.0 


9 11 


132.6 




68.9 


7 9 


32.5 







The heat production as thus computed varies from over twice 
the average two-hour rate to an amount equal to scarcely more than 
one half of the average fasting metabolism of the same animal 
(62 Cals. per two hours). Such fluctuations are entirely inconsistent 
with all data as to the heat production of the body, which, as we 
shall see later, appears to go on with a remarkable degree of uni- 
formity under uniform conditions. The only reasonable conclu- 
sion, then, appears to be that the nitrogen cleavage and the total 
oxidation of the proteids are distinct and at least largely inde- 
pendent processes. 

Gruber's explanation of these facts is substantially as follows: 
It is well established that a relatively constant composition of the 
blood and of the fluids of the body generally is an essential condi- 
* One gram N equivalent to 26 Cals. See Chapter VIII. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. ior 

tion of normal physiological activity. It has been repeatedly 
demonstrated, however, that when the period of growth is past, the 
animal body has not the ability to produce any material amount of 
proteid tissue. A large supply of proteid food, then, necessarily 
tends to alter the composition of the blood and other fluids of the 
body, and the nitrogen cleavage is evidently an effort on the part 
of the organism to counteract this effect by splitting off from the 
proteids a nitrogenous group which can be rapidly excreted, leav- 
ing a non-nitrogenous residue which, so far as it is not immediately 
needed to supply energy, is capable of storage in the relatively inert 
and insoluble forms of glycogen and of fat. 

According to Rosemann,* the rapid increase in the nitrogen ex- 
cretion after a meal arises from two concurrent causes: first, a 
direct stimulus to the proteid metabolism, due to the rapid increase 
of proteids and their digestion products in the blood, which is 
somewhat transitory in character; and, second, the effect of a 
larger relative supply of proteids in causing, according to well- 
known physico-chemical laws, a relatively larger number of mole- 
cules of these substances to enter into reactions with the cell proto- 
plasm. The accompanying graphic representation by Gruber f of 
the course of the nitrogen excretion of a dog on the second day of 



CRMS 


N 




































































































































































































3 


































































































2 




















































































































































1 


















' 1 




^* 


\ 































































































RATE OF NITROGEN EXCRETION PER TWO HOURS. 

feeding with 1000 grams of lean meat and on the three following 
fasting days shows plainly the sudden stimulation of the excretion 

*Loc.cit t Loe. cit., p. 421. 



102 PRINCIPLES OF ANIMAL NUTRITION. 

at first and the fall, rapid at first, and then very gradual, until the 
minimum of the fasting excretion is reached about the third day. 

On the other hand, Rjasantzeff * and Shepski f ascribe the in- 
crease in the nitrogen cleavage after a meal to the increase in the 
digestive work rather than to the proteids as such. They find it 
possible, by stimulating the activity of the digestive organs without 
introducing food, to considerably increase the nitrogen excretion 
in the urine, while, on the other hand, the introduction of proteid 
food through a gastric fistula produced little or no effect. They 
also find the increase with the same amount of food nitrogen to be 
proportional to the (estimated?) amount of digestive work, but seem 
to offer no explanation of the equality of nitrogen cleavage and 
nitrogen supply. 

Cause of Transitory Storage. — As already noted (p. 96), 
any change in the rate of proteid supply in the food, while resulting 
ultimately in a corresponding change in the rate of nitrogen excre- 
tion, gives rise to a transitory gain or loss of nitrogen by the body, 
which was interpreted by Voit as consisting in a corresponding 
change in the stock of "circulatory protein" in the body. The 
facts which we have just been considering permit us to trace some- 
what more fully the details of the phenomenon. Gruber points 
out that while the larger part of the nitrogen cleavage consequent 
upon a single meal of proteids takes place within a few hours, the 
remainder is prolonged over two or three days, as in the case illus- 
trated above, while he likewise shows experimentally that this 
effect is not due to a retention of the nitrogenous metabolic prod- 
ucts, but represents the actual course of nitrogen cleavage. 

Such being the case, the transitory gain or loss incident to a 
change in the rate of proteid supply is most simply explained as 
the result of a superposition of the daily curves. Let it be assumed, 
for example, that 80 per cent, of the nitrogen cleavage incident to 
a single meal of proteids takes place on the first day, 13 per cent, 
on the second, 5 per cent, on the third, and 2 per cent, on the fourth. 
Then if we give, to a fasting animal an amount of proteids contain- 
ing 100 grams of nitrogen for five successive days and then with- 
draw the food, the food nitrogen will be excreted as follows on the 
several days: 

* Jahr. Thier Chem., 26, 349. | Ibid., 30, 711. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 103 





Feeding. 


Fasting. 




1st 
Day. 


2d 
Day. 


3d 
Day. 


4th 
Day. 


5th 
Day. 


1st 
Day. 


2d 
Day. 


3d 
Day. 


From food of 1st day of feeding .... 
" " "2d " " " 

a it tt oj u tt tt 
tt tt tt A+y. tt it tt 

" " "5th " " " 

Total 


80 

'.. 

80 


13 

80 

93 


5 
13 

80 

98 


2 

5 

13 

80 

100 


2 

5 
13 
80 

100 


2 

5 

13 

20 


2 
5 

7 


2 
2 



On the above assumptions, there remained in the body at the 
end of the first day 20 grams of nitrogen in the form of unmeta- 
bolized proteids. At the end of the second day this had increased 
to 27 grams, and at the end of the third day had reached the maxi- 
mum of 29 grams. At the end of the first day's fasting it had fallen 
to 9 grams, at the end of the second day to 2 grams, and at the end 
of the third day to zero. In other words, the transitory storage 
of proteids observed by Voit and others is explained by Gruber as 
due to the fact that the nitrogen cleavage extends over more than 
a single day. 

In reality, of course, the excretion does not take place with any 
such mathematical exactness as in this schematic example, and 
after long fasting in particular a certain rebuilding of proteid tissue 
maj r occur, but the assumed figures may serve to give a general 
notion of the relations of food-supply and excretion. 

In brief, then, we may suppose that when proteid food is given 
to a fasting animal the stimulating effect upon the nitrogen cleavage 
anticipates the use of the proteids for constructive purposes and 
that a large proportion of them is thus destroyed as proteids before 
it can be used to make good the loss of proteids by the organized 
tissues. In other words, the proteids actually available for the 
tissues are much less than the amount supplied in the food. In 
this view of the matter we can readily see why the proteid supply 
overtakes the nitrogen excretion so slowly and why two or three 
times the amount metabolized in fasting is necessary to make good 
the loss from the body and ensure nitrogen equilibrium. 



104 



PRINCIPLES OF ANIMAL NUTRITION. 



Effects on Total Metabolism. 

In the preceding paragraphs the effects of an exclusive proteid 
diet upon the proteid metabolism have been discussed. There 
remain to be considered its effects upon the metabolism of fat. 

Proteids Substituted for Body Fat. — When proteids are 
given to a fasting animal the proteid metabolism is increased, as we 
have seen, but at the same time the loss of body fat is diminished. 

Pettenkofer & Voit * fed a dog with varying amounts of lean 
meat, which may be regarded as consisting chiefly of proteids 
together with small amounts of fat, with the following average 
results in terms of nitrogen: 



Meat Fed, 
Grms. 


Nitrogen 

of Food, 

Grms. 


Nitrogen 

Metabolized, 

Grms. 


Gain or Loss 

of Nitrogen, 

Grms. 


Gain or Loss 
of Fat, 
Grms. 


500 
1000 
1500 % 



17.0 
34.0 
51.0 


5.6 
20.4 
36.7 
51.0 


-5.6 
-3.4 

-2.7 



-95 

-47 
-19 

+ 4 



Rubner § has obtained a similar result by the use of the proteid 
mixture resulting from the extraction of lean meat with water, and 
which still contained some fat. As compared with the fasting state, 
the consumption of 740 grams of the moist material (containing 
72.2 per cent, of water) produced the following effect: 





Nitrogen of Food, 
Grms. 


Nitrogen 

Metabolized, 

Grms. 


Fat 

Metabolized, 

Grms. 


Fasting 

Fed 



35.22 


5.25 

20.37 

+ 21.12 


84.39 
28.37 






Difference 


-56.02 



The increased nitrogen cleavage resulting from an increase in 
the proteid supply liberates a certain amount of energy for the vital 
activities of the body, while the non-nitrogenous residue of the cleav- 

* Zeit f. Biol., 7, 489. 

t Average of first two experiments, p. 84, Chapter IV. 

% Series I only. The others showed a greater gain of fat and of nitrogen. 

§ Zeit. f. Biol., 22, 51. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 105 

age becomes available also as a source of energy to the organism, 
and the metabolism of fat is correspondingly diminished. In 
effect, then, the proteids are simply substituted for more or less of 
the body fat as a source of energy, and Rubner, in a series of experi- 
ments which will be considered in Part II, has shown that the sub- 
stitution takes place, under the condition of these experiments, ap- 
proximately in proportion to the amount of available potential 
energy contained in the proteids and fats respectively. That is, 
if the extra proteids metabolized can supply a certain amount, 
100 Cals., e.g., of energy to the organism, the fat metabolism is 
diminished by a corresponding amount, so that the total expend- 
iture of energy by the body remains unchanged, being simply 
drawn from different sources in the two cases. 

Amount Required to Produce Carbon Equilibrium. — In 
the experiments by Pettenkofer & Voit cited above, the quantity 
of food proteids which resulted on the average in nitrogen equili- 
brium produced substantially an equilibrium also between the 
supply and excretion of carbon. The earlier experiments of Bidder 
& Schmidt * gave similar results. Later experiments, however, 
have given divergent results, nitrogen equilibrium appearing to 
be reached with an amount of proteids which is far from supplying 
sufficient energy for the organism, so that while the stock of pro- 
teids in the body is maintained, its store of fat is still drawn upon. 

We have seen that the proteid metabolism in the normal fast- 
ing animal amounts to 10-14 per cent, of the total metabolism, 
while according to E. Voit (p. 96) the food proteids required for 
nitrogen equilibrium are, roughly, 2\ to 3 times the fasting proteid 
metabolism. It follows, then, that an amount of proteids con- 
taining from 25 to 42 per cent, of the total available energy expended 
by the fasting organism will maintain its store of proteids, and this 
being so, the remaining 58-75 per cent, must necessarily be sup- 
plied by the metabolism of body fat. Thus with the dog on which 
E. Voit's main experiment was made, nitrogen equilibrium was 
approximately reached with 12.05 grams of nitrogen in the food,f 
equivalent to 75.31 grams of protein (NX6.25) and containing 

♦Compare Atwater & Langworthy; Digest of Metabolism Experiments; 
U. S. Dept. of Agr., Office of Experiment Stations, Bui. 45, 388. 
\Loc. tit., p. 69. 



io6 



PRINCIPLES OF ANIMAL NUTRITION. 



approximately, according to Rubner (see Chapter X), 321 Cals. of 
available energy. The actual expenditure of energy by the animal 
was not determined, but is estimated by the author on the basis 
of Rubner's investigations at about 1280 Cals. 

Several experiments by Rubner * lead to the same conclusion. 
In these experiments the carbon and nitrogen of the excreta were 
determined and the nitrogen of the food estimated from average 
figures. The proteid metabolism having been computed from the 
total excretory nitrogen, the corresponding amount of carbon is 
computed from the average composition of the proteids and any ex- 
cess in the excreta is assumed to be derived from the metabolism 
of fat. (Compare p. 78.) The following are the results in brief, 
including the one cited above (p. 104) : 



Food. 



Nitrogen 

of Food, 

Grms. 



Nothing 

415 grms. lean meat 



Nothing 

740 grms. lean meat 



Nothing 

740 grms. extracted lean 
meat 



Nothing 

390 grms. lean meat . . 



Nothing 

350 grms. lean meat 



Nothing 

580 grms. lean meat 



14.11 



25.16 



35.22 



13.26 



11.90 
16! 72 



Nitrogen 

of 

Excreta, 

Grms. 



4.38 
13.72 

2.80 
20.63 

5.25 

26.37 

1.08 
8.53 

1.08 
10.10 

3.50 

18.47 



Fat 
Metab- 
olized, 
Grms. 



Remarks. 



49.33 
25.44 

79.94 
30.73 

84.36 

28.37 

22.88 
11.42 

22.88 
11.79 

37.24 

21.45 



Average of several days. 
1st two days of feeding. 

1st to 4th day of feeding 
1st day of feeding. 
3d to 6th day of feeding. 
1st to 7th day of feeding. 



While some of the experiments were hardly continued long 
enough to absolutely establish the sufficiency of the proteid supply, 
nevertheless we see in all cases a material loss of fat on rations which 
apparently are sufficient to prevent a loss of nitrogen from the 
body. 

It should perhaps be noted that in Pettenkofer & Voit's ex- 
periments 1000 grams of meat nearly prevented a loss of nitrogen 
*Zeit. f. Biol., 22, 43-48; 30, 122-134. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 107 

from the body. It appears possible, then, that nitrogen equilib- 
rium might have been reached with a less amount than 1500 grams, 
and that with this less amount there might still have been a loss of 
fat from the body. Whether this possibility is sufficient to explain 
the apparent discrepancy between these and later results must, 
however, remain a matter of conjecture. 

Utilization op Excess of Proteids. — We have seen that no 
very considerable or long-continued storage of protein takes place 
in the body of the mature animal. However large the supply of 
food proteids, the body very soon reaches the condition of nitrogen 
equilibrium, the outgo of this element in the excreta equaling the 
supply in the food. This fact, as has been pointed out, does not 
necessarily prove that the elements of the food proteids are com- 
pletely oxidized in the organism. As was shown in Chapter II, 
the abstraction from proteid matter of the elements of urea (or, 
more strictly speaking, of the elements found in the urine) leaves 
a very considerable non-nitrogenous residue available for the pur- 
poses of the organism. It was there stated that this residue could 
serve as a source of energy, and likewise that there was good reason 
to believe that sugar was formed from it, while finally the question 
of its ability to serve as a source of fat was reserved for discussion 
in the present connection.' 

Formation of Fat from Proteids. 

Mention has already been made in Chapter II (p. 29) of the fact, 
first asserted by Liebig,* that the animal body manufactures fat 
from other ingredients of its food. As a result of the investiga- 
tions incited by the publication of his views regarding the origin 
of animal fat, Liebig's classification of the nutrients into " plastic " 
and "respiratory" was generally accepted. The proteids were 
regarded as the material for the growth and repair of the muscles 
and the force exerted by the latter was considered to arise from 
their oxidation, while the non-nitrogenous ingredients of the food, 
especially the carbohydrates, were the source of the animal heat, 
and when present in excess gave rise to a production of fat. 

As time went on, however, observations began to accumulate 

* Compare p. 163. 



108 PRINCIPLES OF ANIMAL NUTRITION. 

tending to show that the proteids were not without influence on 
fat-production. 

As early as 1745 R. Thomson,* in experiments on inilch cows, 
noted an apparent connection between the supply of proteids in 
the food and the production of butter. 

Hoppe t in 1856 interpreted the results of an experiment in 
which a dog was fed lean meat with and without the addition of 
sugar as showing a formation of fat from proteids. The same 
author % hi 1859 claimed to have shown a slight formation of fat 
from casein in milk exposed to the air, and this was confirmed later 
by Szubotin.§ The latter author, and also KemmerichJ and later 
Voit,!' experimented upon the production of milk-fat by dogs. 
Their results, while indicating the possibility of a formation of fat 
from proteids, were indecisive. 

Pettenkofer & Voit's Experiments. — Carl Voit, however, 
was the first to distinctly champion the new theory, and aside from 
certain confirmatory facts,** such as the formation of fatty acids in 
the oxidation of proteids, the formation of adipocere, the alleged 
formation of fat from proteids in the ripening of cheese and in the 
fatty degeneration of muscular tissue, especially in cases of phos- 
phorous poisoning, — facts not all of which are fully established and 
whose importance in this connection has probably been over- 
estimated, — the evidence bearing on the question of the formation of 
fat from proteids has been until recently largely that supplied by 
the famous researches of Pettenkofer & Voit ft at Munich. 

In these experiments a dog weighing about 30 kgs. was fed 
varying amounts of prepared lean meat from which fat, connective 
tissue, etc., had been removed as completely as was possible by 
mechanical means. The material thus prepared, while still con- 
taining small amounts of fat, etc., was as near an approach to an 
exclusively proteM diet as was practicable, it having been found 
impossible to successfully carry out feeding experiments with pure 

* Ann. Chem. Pharm., 61, 228. JVirchow's Archiv, 17, 417. 

tVirchow's Archiv, 10, 144 %Ibid., 36, 561. 

|| Wolff, Ernahrung Landw. Nutzthiere, p. 351. 

IZeit. f. Biol., 5, 136. 

** Compare Voit's summary in 1S69, Zeit. f. Biol., 5, 79-169. 

ft Am. Chem. Pharm., II, Suppl. Bd., pp. 52 and 361 ; Zeit. f. Biol., 5, 
106; 7, 433. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 109 

proteids. The experiments were conducted with the aid of a respi- 
ration apparatus, the gain or loss of proteids and fat being com- 
puted from the nitrogen and carbon balance in the manner described 
in Chapter III. 

The following is a condensed summary of the average results 
of these experiments, as given by the authors,* but includes also 
the average of all the experiments with 1500 grams of meat. On 







Gain (+) or Loss (-) by Animal. 


Number of 


Meat Eaten per Day, 






Experiments. 


Grins. 










Flesh. 


Fat. 






Grms. 


Grins. 







-165 


-95 




500 


- 99 


-47 




1000 


- 79 


-19 


3t 


1500 





+ 4 


22 


1500 


+ 18 


+ 9 


1 


1800 


+ 43 


+ 1 


2 


2000 


- 44 


+ 58 


1 


2500 


- 12 


+ 57 



the smaller rations, which were obviously insufficient for main- 
tenance, the animal lost both flesh and fat. A ration of 1500 
grams of meat per day sufficed approximately to maintain the ani- 
mal as regards flesh and to cause a small gain of fat. On the 
heavier rations the excretion of nitrogen kept pace with the supply 
in the food in the manner illustrated on pp. 94-96 but the excretion 
of carbon fell considerably below the supply, indicating a produc- 
tion of fat. 

It is to be noted that only the last three experiments in the above 
table actually show any very considerable production of fat. The 
insufficient rations naturally do not, and while among the twenty- 
two trials with 1500 grams of meat the majority appear to show a 
formation of fat, the amount is usually comparatively small, and 
in two cases a loss was observed. On the whole, however, the evi- 
dence of this series of experiments has been generally accepted as 
conclusive in favor of the formation of fat from proteids. 

Pfluger 's Recalculations. — One very important point, how- 
ever, has until recently been overlooked. The evidence is based on 

* Zeitschr. f . Biol., 7, 489. 
I Series 1 only. 



HO PRINCIPLES OF ANIMAL NUTRITION. 

a comparison of the income and outgo of carbon and nitrogen. 
Pfliiger,* however, has called attention to the fact that while Pet- 
tenkofer & Voit made direct determinations of the outgo of these 
elements, or at least of the principal factors of it, the income is not 
computed from actual analyses of the meat used, but upon the 
assumption of average composition. According to Pfliiger, not 
only are the possible variations from the average in individual 
experiments a serious source of error, but the average itself is 
erroneous, the percentage of carbon assumed in the meat being 
too high. Pettenkofer & Voit estimate the ratio of nitrogen to 
carbon in lean meat f as 1 : 3.684, while according to Pfliiger it is 
not higher than 1 : 3.28, and probably lower. Moreover, Petten- 
kofer & Voit failed to take due account of the fact that a part of 
the gain of carbon which they observed could be ascribed to the fat 
still contained in the prepared "lean" meat. Another, although 
slight, source of error, according to Pfliiger, lies in the fact that 
the carbon in the urine was estimated from the amount of nitrogen 
found by analysis on the assumption of a ratio of 1:0.60, while it 
should be 1:0.67. 

Using the above corrections, Pfliiger has recalculated twenty- 
four of the experiments by Pettenkofer & Voit, which have been 
generally accepted as demonstrating the formation of fat from pro- 
teids, with the results shown on the opposite page .J 

In the great majority of cases the experiments as recalculated 
show a loss instead of a gain of fat, and in three of the four cases in 
which a gain still appears it is small in amount, and, as Pfliiger 
believes, within the limits of experimental error. Naturally such 
calculations as the above can neither prove nor disprove the hypoth- 
esis that the proteids serve as a source of fat. They simply show 
that the experiments which have served as the principal support 
for that hypothesis do not demonstrate what they were supposed 
to. The question turns largely upon the elementary composition 
of the meat used by Pettenkofer & Voit, which they failed to 
determine. It is manifestly impossible to repair this error now, 

* Arch. ges. Physiol., 51, 229. 

f Including such fat as cannot be removed by mechanical means. 
\Loc. tit., p. 267. The experiments which showed a loss of fat as origi- 
nally computed are omitted. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. in 





Meat Eaten 

per Day, 

Grms. 


Gain (+) or Loss (— ) of Fat. 


Date of Experiment. 


According to Pet- 

tenkofer & Voit. 

Grms. 


According to 
Pfliiger. 
Grms. 


Feb. 19, 1861 


1800 
2500 
1500 
1500 
1500 
1500 
1500 
1500 
1500 
1500 
1500 
1500 
1500 
1500 
1500 
1500 
1500 
1500 
1500 
1500 
2000 
2000 
1500 
1500 


+ 1.4 

+ 56.7 
+ 3.4 
+ 7.3 
+ 34.4 
+ 20.7 
+ 35.9 
+ 22.9 
+ 8.7 
+ 17.4 

0.0 
+ 9.9 
+ 2.1 
+ 14.3 

0.0 
+ 13.8 
+ 9.0 
+ 12.7 
+ 26.3 
+ 29.1 
+ 55.9 
+ 58.5 
+ 11.9 
•+9 4 


35 8 


Apr. 3, " 


+ 3.93 
29 3 


Mch. 4, 1862 


"21, " 


—23 4 


Apr. 7, " 


+ 3.7 
— 11 1 


"12, " 


"14, " 


+ 3.8 

— 8 4 


"16, " 


Aug. 6, " . .. 


— 13 5 


" 8, " 


— 8 3 


Feb. 20, 1863 


—31 6 


"23, " 


—22 1 


" 27 " 


—24 4 


Mch. 4, " 


— 16 9 


Apr. 1, " 


—31 8 


" 7, " 


— 17 5 


"10, " 


—22 


June 1, " 


— 13 


" 8, " 


— 5 4 


"12, " 


— 2 9 


"21, " 


+ 13 6 


" 26 * " 


+ 16 


July 3, " 


—20 6 


" 6, " 


—23 7 









and since Pfluger's estimates seem to be at least as trustworthy as 
Pettenkofer & Voit's, and lead to exactly the opposite results, the 
only verdict possible, so far as these experiments are concerned, is 
"Not proven." 

Later Experiments. — Shortly after the publication of Pfluger's 
critique, E. Voit,f in a preliminary communication, presented the 
results of investigations upon this question undertaken in the 
Munich laboratory. So far as the writer is aware, no complete 
account of these experiments has yet appeared, but the data given 
by Voit in the preliminary account show a retention in the body 
of 8 to 10 per cent, of the carbon of the metabolized proteids, and 
to this extent confirm the earlier results obtained by his father. 
He believes the observed gain of carbon to be too great to be 
accounted for by the storage of glycogen and interprets it as 
showing a production of fat from proteids. 

* Includes a correction of Pettenkofer & Voit's figures for the urinary 
nitrogen, hoc. cit. p. 263. 
•j-Thier. Chem. Ber., 22, 34. 



H2 PRINCIPLES OF ANIMAL NUTRITION. 

Kaufmann likewise interprets the results of the respiration ex- 
periments cited in another connection on p. 99 as demonstrating 
the production of fat from proteids, but in view of the brevity of 
the experiments (five hours), and the fact that they covered the 
period of most active nitrogen cleavage, this conclusion seems 
hardly justified. 

Cremer * has reported the results of an experiment upon a cat 
which he regards as showing a formation of fat from proteids. The 
animal, weighing 3.7 kgs., passed eight days continuously in the 
respiration apparatus and received per day 450 grams of lean 
meat. No complete nitrogen and carbon balance is reported. The 
average daily excretion of nitrogen was 13 grams. Assuming the 
ratio of nitrogen to carbon in fat and glycogen-free flesh to be 1 :3.2,f 
this corresponds to 41.6 grams of carbon in the form of proteids, 
while the total excretion of this element was only 34.3 grams, thus 
showing a retention by the organism of 7.3 grams per day. The 
body of the animal at the close of the experiment was found to con- 
tain not more than 35 grams of glycogen and sugar, while the ob- 
served gain of carbon during the eight days was equivalent to 
about 130 grams of glycogen. It is therefore concluded that fat 
was formed from proteids. In three other experiments, with an 
abundant meat diet, it is computed that from 12.6 to 17.0 per cent, 
of the carbon of the metabolized proteids was stored in the body. 

Gruber \ has recently reported two experiments, dating from 
the year 1882, in which a dog was fed 1500 grams per day of lean 
meat. The nitrogen of feces and urine were determined daily 
for six and eight days respectively and the carbon dioxide of the 
respiration on five days in each experiment; the carbon of urine 
and feces and of the metabolized proteids was computed from the 
nitrogen, using for the carbon of the proteids the factor 3.28. The 
excretion of nitrogen approximately equaled the supply, especially 
on the later days of the experiments, but from 10 to 15 per cent, 
of the carbon was unaccounted for in the excreta. The total reten- 
tion of carbon during the experiments, together with the equivalent 
quantities of glycogen, were: 

*Jahresb. Agr. Chem., 40, 538; Zeit. f. Biol, 38, 309. 

f Kohler (Zeit f. physiol. Chem., 31, 479) found an average of 1:3.16 for 
the fat-free flesh of cattle, swine, sheep, rabbits, and hens. See p. 64. 

% Zeit f Biol., 42, 409. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 113 





Carbon. 


Equivalent Glycogen. 


Experiment 1, seven days 

2, eight " 


113.9 Grms. 
195.9 " 


256.3 Grms. 
441.0 " 



These amounts of glycogen are much greater than have ever 
been found in the body of a dog of this weight (about 20 kgs.), and 
the larger part of the storage of carbon must therefore have been 
in the form of fat. 

In addition to the above results on normal animals, Polimanti * 
has reported experiments apparently showing a formation of fat 
from proteids in phosphorous poisoning. The latter investigation, 
as well as those of Cremer and of E. Voit, have been the subjects of 
searching criticism by Pfl tiger, f who claims to have shown the in- 
sufficiency of the experimental evidence adduced, but it is impos- 
sible here to enter into the details of these controversial articles. 
Negative results have also been reported by Kumagawa & 
Kaneda.J Rosenfelt,§ Taylor, || Athanasiu,!" and Lindemann,** but 
in a matter of this sort negative evidence naturally carries much 
less weight than positive, and on the whole there would appear 
to be good reason for still regarding the proteids as a possible 
source of fat. 

Difficulty of Proof. — A serious difficulty in the way of an 
unquestionable demonstration of this possibility lies in the limited 
amount of proteids which an animal can consume. As we have 
seen, a relatively large supply of them is necessary even to produce 
nitrogen equilibrium, and a still further large addition is required to 
supply the demands of the organism for energy. Only the proteids 
supplied in excess of this latter amount are available for fat produc- 
tion, and thus it comes about that the limit of consumption and 
digestion by the animal is reached before any very large produc- 
tion of fat can take place. 

On the other hand, if non-nitrogenous nutrients (carbohydrates 

* Arch. ges. Physiol., 70, 349. 

■\Ibid., 68, 176; 71, 318. 

JU. S. Dept. Agr., Expt. Station Record, 8, 71. 

§Jahresb. Physiol., 6, 260. 

|| Ibid.. 8, 249, Jour Exper. Medicine, 4, 399. 

T[Arch. ges. Physiol., 74, 511. 

**Zeit. f. Biol., 39, 1. 



H4 PRINCIPLES OF ANIMAL NUTRITION. 

for example) are employed to supply a part of the necessary energy,. 
a more abundant fat production may be caused but the results 
are ambiguous, since it is possible that the non-nitrogenous residue 
of the proteids may be metabolized to furnish energy otherwise 
supplied by the non-nitrogenous nutrients and that the actual 
material for the formation of fat may come from the latter. 

That proteids added to a mixed ration may give rise to a large 
amount of fat has been strikingly shown by Kellner * in experi- 
ments on oxen in which wheat gluten was added to a fattening 
ration. Approximately 198 grams of fat were produced for each 
kilogram of protein fed, but to the writer the reasoning by which 
Kellner seeks to prove that this fat must have been derived directly 
from the proteids seems inconclusive. 

Finally, as was indicated in Chapter II (p. 50), the apparently 
well-established fact that the metabolism of proteids in the body 
gives rise to the formation of carbohydrates (or at least may do so), 
together with the further fact that fat is undoubtedly formed from 
carbohydrates, renders it difficult to assign any reason why the non- 
nitrogenous residue of the proteids should not supply material to 
the cells of the adipose tissue for the production of fat. 
§ 2. The Non-nitrogenous Nutrients. 
Effects on the Proteid Metabolism. 

The relations between proteid metabolism and proteid supply 
which have been outlined in the preceding section, while deduced 
mainly from experiments in which the food consisted substantially 
of proteids only, are of general applicability, yet are subject to im- 
portant modifications in the presence of non-nitrogenous nutrients. 

Tend to Diminish Proteid Metabolism. — As was first shown 
by C. Voit, the addition of non-nitrogenous nutrients to a ration 
consisting of proteids tends to render the proteid metabolism less 
than it otherwise would be. The effect is common to the fats and 
carbohydrates, although with some differences in details. 

Fats. — The following example, taken from Voit's experiments,! 
illustrates in a somewhat marked way the influence of the addition 
of fat to proteid food upon the excretion of nitrogen. A dog con- 
suming daily 1000 grams of lean meat received in addition on two 
days 100 and 300 grams of fat, with the following results: 
* Landw. Vers. Stat., 53, 456. 
t Zeit. f. Biol., 5, 334. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. nj 





Food per Day. 


Urea per Day, 
Grms. 




Meat, 
Qrms. 


Fat, 
Grms. 


July 31 


1000 
1000 
1000 
1000 



100 
300 




81 7 


Aug. 1 


74 5 


" 2 


69 3 


" 3 


81 2 







In the whole series of eight experiments with varying amounts 
of meat and fat the decrease in the excretion of urea ranged from 1 
per cent, to 15 per cent, of the amount supplied in the food, averag- 
ing about 7 per cent. With the same amount of fat in the food 
the decrease in the excretion of urea was not ; as a rule, greater with 
large than with moderate rations of meat. On the other hand, 
with a small proteid supply in the food the production of urea was 
sometimes increased slightly by the addition of much fat, and the 
same result was observed to a more marked extent when fat alone 
was given to fasting animals. With medium rations of meat, in- 
creasing the fat supply had usually little effect, but with heavy 
meat rations it tended to further diminish the excretion of urea. 

Subsequent investigation has fully established this tendency 
of fat to diminish the proteid metabolism, and the fact is too well 
known to require extended illustration here. As a recent instance 
may be cited the following results obtained by Kellner * in experi- 
ments upon oxen, in which oil was added to a basal ration: 





Nitrogen Digested. 


Nitrogen in Urine. 




Basal Ration, 
Grms. 


Basal Ration + Oil, 
Grms. 


Basal Ration, 
Grms. 


Basal Ration -\- Oil, 
Grms. 


OxD 

Ox F 


135.30 
111.67 

86.27 


134 . 55 
109.17 

87.08 


122 . 54 

106.03 

86.30 


120.38 
89.27 


Ox G 


79.83 







Carbohydrates. — -The effects of the readily soluble hexose 
carbohydrates (starch and the sugars) have been quite fully inves- 
tigated, while as to those of the less soluble carbohydrates, particu- 
larly of the five-carbon series, considerable diversity of opinion 
still prevails. 

* Landw. Vers. Stat., 53, 121 and 210. 



I if) 



PRINCIPLES OF ANIMAL NUTRITION. 



Starch and Sugars. — The investigations of C. Voit * show that 
starch or sugar added to a proteid diet causes, as does fat, a decrease 
in the elimination of urea. Voit found an average decrease of 
about 9 per cent, in the proteid metabolism, the extremes being 5 
and 15 per cent, with varying amounts of carbohydrates. An in- 
crease in the carbohydrates, the proteid food remaining the same, 
tended to further diminish the excretion of urea. The following 
examples illustrate this effect of the carbohydrates. When given 
to a fasting animal, carbohydrates did not, as in the case of fat, 
cause an increase in the proteid metabolism. 





Food. 


Urea 




Meat, 
Grms. 


Carbohydrates, 

Grms. 


per Day, 
Grms. 


June 23-July 2, 1859 

July 2-5, " 


500 
500 


300-100 



35.4 
39.9 






July 4-10, 1864 

" 10-19, " 


800 
800 
800 




100-400 




59.1 
54.5 


" 19-20, " 


63.8 






July 23-26, 1864 


1000 
1000 
1000 




100-400 




73.5 


" 26-28, " 


64.4 


" 28-Aug. 1,1864 


79.6 


June 29-July 8, 1863 


1500 
1500 



200 


114.9 


July 8-13, " 


103.3 






Jan, 6, 1859 


2000 
2000 



200-300 


143.7 


" 7-11, 1859 


131.0 







This effect of the carbohydrates, like that of fat, has been abun- 
dantly confirmed by later investigators and is one of the well-estab- 
lished facts of physiology. Weiske f in particular has investigated 
the effect of the non-nitrogenous nutrients upon the metabolism 
of sheep, while Miura J and Lusk § have shown that the abstraction 
of carbohydrates from the diet of a man results in a marked increase 
in the proteid metabolism. The following data, taken from Refi- 
ner's extensive respiration experiments at Mockern, illustrate the 
same effect of starch in the case of cattle : 

* Zeit. f. Biol., 5, 434. 

t Zeit. physiol. Chem. 21, 42; 22, 137 and 265. 

% v. Noorden, Pathologie des Stoffwechsels, p. 117. 

§ Zeit. f. Biol., 27, 459. 



THE RELATIONS OF METABOLISM TO FOOD SUPPLY. 117 





Nitrogen Digested. 


Nitrogen in Urine. 




Basal Ration, 
Grms. 


Basal Ration 

-+- Starch, 

Grms. 


Basal Ration 
Grms. 


Basal Ration 

+ Starch, 

Grms. 


OxD 


135.30 
111.67 
86.27 
116.51 
128.11 


118.40 

107.55 

80.92 

94.66 

118.18 


122.54 
106.03 
86.30 
109.28 
122.62 


104.69 


Ox F 


81.18 


Ox G 


63.83 


Ox H 


81.71 


Ox J 


103.13 







Since the addition of starch to the basal ration diminished the 
apparent digestibility of the protein, the effect is most clearly seen 
by comparing the daily gains of nitrogen by the animals on the 
two rations, as follows: 





On Basal Ration, 
Grms. 


With Addition 

of Starch, 

Grms. 


Difference. 


Ox D 


12.76 

5.64 

-0.03 

7.23 

5.49 


13.71 
26.37 
17.09 
12.95 
15.05 


+ 0.95 


Ox F 


+ 20.73 


Ox G 


+ 17.12 


Ox H . . . 


+ 5.72 


Ox J 


+ 9.56 







Cellulose. — The peculiar position occupied by cellulose, as the 
essential constituent of the "crude fiber" of feeding-stuffs, in the 
nutrition of domestic animals causes much interest to attach to the 
study of its effects upon metabolism. We shall consider here only 
its effects upon the proteid metabolism. 

The first to take up this subject appears to have been v. Knie- 
riem,* who experimented upon rabbits. In a preliminary experi- 
ment the addition of prepared " crude fiber " to a basal fiber-free 
ration in which the necessary bulk was obtained by the use of horn- 
dust f gave the following results for the urinary nitrogen per day; 

I. Without fiber 0.9034 grams 

II. With 9.284 grams fiber . 7618 " 

III. Withoutfiber 0.7560 " 

The low figure for the third period is ascribed to the effect of 
the crude fiber still remaining in the digestive tract. In a follow- 
ing series, in which respiration experiments were also made, the 
following results per day were obtained for the nitrogen : 

* Zeit. f. Biol., 21, 67. t Shown to have been entirely indigestible. 



n8 



PRINCIPLES OF ANIMAL NUTRITION. 



Period. 


Food per Day. 


Nitrogen 

of Food, * 

Grms. 


Nitrogen 

of Excreta * 

Grms. 


Gain of 

Nitrogen, 
Grms. 




Milk and horn dust 


2.75 
2.75 
2.70 
2.70 
2.70 


3.35 
2.65 
3.03 
3.02 
2.73 


-0.60 


II. 10 days. 


Same + 22 grms. crude fiber . . . 
Milk and horn dust 


+ 0.10 
-0.33 


IV. 4 days. 

V. 3 days.t 


Same + 11 grms. cane sugar . . . 
" + 33 " " " ... 


-0.32 
-0.03 



Weiske % disputes v. Knieriem's conclusion that cellulose dimin- 
ishes the proteid metabolism. He experimented upon a sheep, 
which was fed in a first period exclusively on beans. In succeeding 
periods the effect upon the proteid metabolism of adding to this 
ration, first, inferior oat straw, and second, starch was tested, the 
bean ration being diminished slightly in these periods in order 
to keep the total digestible protein of the ration as nearly uniform 
as possible. On the basis of a preliminary digestion trial with the 
straw, the quantity of starch was so adjusted as to supply, in Period 
III, according to computation, an amount of digestible carbohy- 
drates equal to the digested fiber and nitrogen-free extract of the 
straw of Period II, while in Period V it equalled the digested 
nitrogen-free extract only. Actual determinations of the digesti- 
bility of the mixed rations showed that this equality was approxi- 
mately, although not exactly, reached, the amount of digested 
starch being rather less than the computed amount. 

The results as regards the proteid metabolism as originally re- 
ported by Weiske are given in the first portion of the table on 
the opposite page. v. Knieriem,§ having criticised the results on 
the ground that the metabolic nitrogen of the feces was not taken 
into account, and that when this was done the experiments made a 
more favorable showing for the digested crude fiber, Weiske || has 
recalculated his results on the assumption that the feces contained 
0.4 grams of metabolic nitrogen for each 100 grams of dry matter 
digested, "|[ with the results shown in the second half of the table. 

* Not including that of the horn dust. 

t Results regarded by the author as of doubtful value 

% Zeit, f. Biol., 22, 373. 

%Ibid., 24, 293. 

|| Ibid., 24, 553. 

^[Compare Kellner, Landw. Vers. Stat., 24, 434; and Pfeiffer, Jour. f. 
Landw., 33, 149. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 119 





Ration. 


Uncorrected. 


Corrected. 


■0 



'Eh 
<U 

Ah 


Nitro- 
gen 
Appar- 
ently 
Di- 
gested. 


Nitro- 
gen 
of 
Urine. 


Gain. 


Com- 
puted 
Nitro- 
gen 
Di- 
gested. 


Nitro- 
gen 
of 
Urine. 


Gain. 


I. 

II. 


500 grms 
j 490 " 
\ 515 " 


beans .... 
beans ) 
straw \ ' 


Grms. 
20.51 

19.58 


Grms. 
20.93 

16.82 


Grms. 
-0.42 

+ 2.76 


Grms. 
22.02 

21.78 


Grms. 
20.93 

16.82 


Grms. 
+ 1.09 

+ 4.96 


IV. 


j 490 " beans ) 
I 515 " straw j" ■ - 

Average of II. and IV . 


18.81 


17.26 


+ 1.55 


21.09 


17.26 


+ 3 


83 








+ 2.16 






+ 4 


40 




(510 grms 


beans ) 
















III. 


\ 180 ' 
( 20 ' 
I 500 "' 




starch > . . 
sugar ) 
beans ) 


20.03 


14.94 


+ 5.09 


22.16 


14.94 


+ 7 


22 


V. 


■I 90 ' 
( 10 ' 




starch j- . . 
sugar ) 


20.64 


17.75 


+ 2.89 


22.43 


17.75 


+ 4 


68 



It will be seen that the experiments make substantially the 
same showing for the relative effects of cellulose and starch whether 
we take the uncorrected results or eliminate so far as possible the 
effects of the greater amount of food in the later periods upon the 
excretion of metabolic products in the feces. The addition of starch 
and sugar in Period III produced about twice as great an effect in 
reducing the proteid metabolism as did a somewhat larger amount 
of digestible fiber and nitrogen-free extract from straw in Periods 
II and IV. In Period V the starch added was only equal to the 
digested nitrogen-free extract of the straw in Periods II and IV. 
'Since the effect upon the proteid metabolism is substantially the 
same, Weiske concludes that the nitrogen-free extract of the 
straw, which has the elementary composition of starch, is equal to 
it in its effect upon the proteid metabolism, and that the digested 
crude fiber is valueless in this respect. It must be said, however, 
that this latter conclusion is not warranted by the facts, since it 
rests upon the unproved assumption of equality of nutritive value 
(in respect of the proteid metabolism, at least) of starch and the 
nitrogen-free extract of the straw. Weiske also experimented 
with rabbits, finding in one case no effect upon the proteid metab- 
olism and in the second an increase of it, as a result of adding crude 
fiber to a fiber-free ration. 



120 PRINCIPLES OF ANIMAL NUTRITION. 

Lehmann * experimented upon a sheep by adding respectively 
crude fiber, prepared from wheat straw, and starch to a basal ration. 
The results were not entirely sharp but showed plainly a decrease 
of the proteid metabolism on the crude fiber ration which was 
equal approximately to 61 per cent, of that secured by the use of 
starch. In a second series of experiments, Lehmann and Vogel t 
compared the effects upon the proteid metabolism of sheep of cane- 
sugar and of the digestible non-nitrogenous matters of oat straw. 
On the basis of a very careful discussion of the experimental errors, 
they show that the latter substances have a marked effect in diminish- 
ing the proteid metabolism, and in particular that if we ascribe this 
effect exclusively to the digested nitrogen-free extract, as Weiske 
does, we must admit that the latter produced an effect from two 
to nine times as great as that of cane-sugar. They therefore con- 
clude that their results show qualitatively an effect of the digested 
cellulose upon the proteid metabolism. Reckoning the digested 
nitrogen-free extract of the straw as equivalent to sugar, they com- 
pute from the average of all their experiments that the cellulose 
produced 75.7 per cent, as great an effect as the sugar, but they do 
not regard this quantitative result as well established. 

Holdefleiss J experimented upon two sheep, feeding in a first 
period meadow hay exclusively. In the second period one half of the 
hay was replaced by a mixture of peanut cake, starch, and a little 
sugar, while in the third period the starch was replaced by paper 
pulp. In one case a fourth period was added in which the paper 
pulp and sugar were simply omitted from the ration. The digested 
nutrients and the proteid metabolism per day are tabulated on p. 121. 

Converting the small differences in the amount of crude fat 
digested into their equivalent in nitrogen-free extract by multipli- 
cation by the factor 2.5, Holdefleiss computes from a comparison 
of the second and third periods that the digested crude fiber pro- 
duced on the first animal 80.1 per cent, and on the second animal 
84.2 per cent, of the effect of the starch. A somewhat higher value 
would be obtained from a comparison of the first and second periods 
in the case of Sheep II, while on the other hand a comparison of the 
corresponding periods with Sheep I gives a much lower value, and is 

* Jour. f. Landw., 37, 267. t Ibid., 37, 281. 

J Bied. Centr. Bl. Ag. Chem., 25, 372. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 121 



Ration. 



Apparently Digested. 



Crude 

Fat, 
Grms. 



Crude 
Fiber, 
Grms. 



N. fr. 

Extract, 

Grms. 



Nitro- 
gen, 
Grms. 



Nitro 
gen of 
Urine, 
Grms. 



Gain 

of 
Nitro- 
gen, 
Grms. 



Sheep I. 

Period 1 

" 2 



" 4 
Sheep II. 
Period 1 

" 2 



Hay only 

Hay, peanut cake, sugar, 

and starch 

Hay, peanut cake, sugar, 

and paper pulp 

Hay and peanut cake 

Hay only 

Hay, peanut cake, sugar, 

and starch 

Hay, peanut cake, sugar, 

and paper pulp 



13.55 

15.27 

13.67 
18.57 

11.76 

13.07 

15.14 



315.72 

134.11 

439.32 
171.12 

171.92 

77.48 
235.31 



470.85 

560.71 

320.21 
345.92 

276.42 

336.62 

198.46 



15.02 

13.55 

13.76 
16.25 

10.88 

9.54 

8.82 



13.83 

11.31 

11.26 
14.45 

8.45 

7.85 

7.62 



1 19 

2.24 

2.50 
1.80 

2.43 

1.69 

1.20 



even consistent with the view that cellulose has no effect upon 
the proteid metabolism. In other words, the results on Sheep I, in 
the first period, appear inconsistent with the other results. 

Kellner * has experimented with rye straw extracted with an 
alkaline liquid under pressure in the same manner as in paper- 
making and containing 76.78 per cent, of "crude fiber" and 19.96 
per cent, of nitrogen-free extract. The results as regards the pro- 
teid metabolism, compared with those on starch, are given in the 
upper table of p. 122. 

Taking the figures as they stand, and attempting no correction 
for the marked depression in the apparent digestibility of the nitro- 
gen resulting from the addition of the extracted straw or starch, 
they show a considerable effect by both in diminishing the proteid 
metabolism relatively to the supply in the food and thus causing 
an increased gain of nitrogen by the body. Any correction for the 
metabolic nitrogen of the feces, as in Weiske's experiments, would, 
of course, tend to make the effect appear still greater. With the 
first animal, after taking account as well as possible of the slight 
differences in the fat digested in both periods and of the slight 
effect of the starch upon the digestibility of the fiber of the basal 
ration, the digestible matter of the extracted straw, five sixths of 
which was cellulose, appears to have produced more than twice 
as great an effect as an equal amount of starch. With the second 
* Landw. Vers. Stat., 53, 278. 



PRINCIPLES OF ANIMAL NUTRITION. 







Apparently Digested. 


Nitrogen 

of Urine, 

Grms. 


Gain of 




Crude 

Fat, 

Grms. 


Crude 
Fiber, 
Grms. 


N. fr. 

Extract, 
Grms. 


Nitrogen, 
Grms. 


Nitrogen 
Grms. 


OxH. 
Period 5 
« 4 


Extracted straw. . 
Basal ration 

Starch 


116 
101 


3129 
1083 


3351 
2912 


102.47 
116.51 


76.31 

109.28 


26.16 
7.23 


" 3 


15 

92 
101 


2047 

1057 
1083 


439 

4773 

2912 


-14.04 

94.66 
116.51 


-32.97 

81.71 
109.28 


18.93 
12 95 


" 4 


Basal ration 

Difference 

Extracted straw. . 
Basal ration 

Difference 

Starch 


7.23 


Ox J. 
Period 5 

" 4 


-9 

110 

107 


-26 

3101 
1114 


1861 

3344 

2895 


-21.85 

112.19 
128.11 


-27.57 

95.80 
122 . 62 


5.72 

16.39 
5.49 


" 3 


3 

85 
107 


1987 

1105 
1114 


449 

4396 
2895 


-15.92 

118.18 
128.11 


-26.82 

103.13 
122.62 


10.90 
15 05 


" 4 


Basal ration 

Difference 


5.49 




-22 


-9 


1501 


-9.93 


-19.49 


9.56 



animal, on the contrary, the effect of the digested matter of the ex- 
tracted straw was but little more than two thirds that of the starch. 
Ustjantzen * has recently reported the results of an experiment 
upon a sheep substantially like those of Weiske (p. 118), a basal 
ration of beans receiving, in succeeding periods, additions of meadow 
hay, rice, or sugar, the two latter being computed to supply an 
amount of digestible carbohydrates equal to the digestible nitrogen- 
free extract supplied by the hay. The increased amounts of crude 
fiber and nitrogen-free extract digested and the resulting increases 
in the gain of nitrogen by the animal were as follows : 



From hay ration 
" rice " 
" sugar " 



Crude Fiber, 
Grms. 



108.60 

-2.53 

5.07 



Nitrogen -free 

Extract, 

Grms. 



95.55 
107.15 
109.20 



Gain of 

Nitrogen, 

Grms. 



3.33 
2.90 
2.59 



It appears that, as in Weiske's experiments, the carbohydrates 
of the rice and sugar produced nearly as great an effect upon the 
* Landw. Vers. Stat., 56, 463. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 123 

gain of nitrogen as the total non-nitrogenous matter digested from the 
hay, and the author follows Weiske in concluding that the digested 
crude fiber producd but little effect on the proteid metabolism. 

The same author also reports experiments upon a rabbit similar 
to those of v. Knieriem, crude fiber prepared from hay being added 
to a basal ration of peas, with the following results, which show 
practically no effect of the crude fiber upon the proteid metabolism : 





Nitrogen 

of Food, 

Grms. 


Nitrogen Excreted. 


Gain of 


Food. 


Urine, 
Grms. 


Feces, 
Grms. 


Total, 
Grms. 


Nitrogen. 
Grms. 


Peas 

" and 5 grams, crude fiber. . . . 

" " 5 " sugar 

" " 6.5" crude fiber... . 


0.845 
0.857 
3.845 
0.860 


0.855 
0.821 
0.701 
0.899 


0.016 
0.120 
0.080 
0.170 


0.871 
0.941 
0.781 
1.069 


-0.026 
-0.084 
+ 0.064 
-0.209 



While it is obviously unsafe to draw any positive conclusions 
regarding the relative effect of cellulose and the more soluble carbo- 
hydrates from the various experiments cited above, the balance 
of evidence seems clearly to show that their influence upon the pro- 
teid metabolism is qualitatively the same, while it appears on the 
whole probable that digested cellulose is at least not greatly in- 
ferior quantitatively to digested starch. 

Organic Acids. — Certain methods of preparing or preserving 
fodder, notably ensilage, result in the formation of not inconsider- 
able amounts of organic acids. Moreover, it appears that these acids 
are normally produced in considerable quantities in the herbivora 
by the fermentation of cellulose and other carbohydrates, and that 
fact naturally leads to a consideration of their effects upon meta- 
bolism as compared with the latter substances. 

We have seen (p. 27) that the organic acids are oxidized in the 
body, and it therefore seems natural to suppose that they may 
influence the proteid metabolism. This question has been investi- 
gated by Weiske & Flechsig.* After some only partially success- 
ful experiments on a rabbit, they fed a sheep with a basal ration 
(of hay, starch, cane-sugar and peanut cake) containing a liberal 
supply of protein and having a nutritive ratio of 1 : 3.4. To this 
ration there was added in succeeding periods lactic acid as calcium 
lactate, acetic acid as sodium acetate, and for comparison dextrose. 
*Jour. f. Landw., 37, 199. 



T24 



PRINCIPLES OF ANIMAL NUTRITION. 



Disregarding for our present purpose the slight effect of these sub- 
stances upon the digestibility of the non-nitrogenous ingredients 
of the ration the results were: 





Nitrogen 

Digested, 

Grms. 


Nitrogen 

of Urine, 

Grms. 


Gain of 

Nitrogen, 

Grms. 




18.06 
17.83 

18.03 

18.69 
17.69 

17.93 

18.70 

[18.70*] 


17.56 
15.60 

15.72 

16.85 
15.29 

12.86 

16.54 

17.04 


0.50 


" " -\- 60 grms. lactic acid 


2.23 


ii +120 « " « ) 
(Three days only.) ) 


2.31 
1.84 


" " -j- 60 grms. dextrose 


2.40 


" +120 " " ) 
(Three days only.) f 


5.07 
2.16 


" " + 60 grms. acetic acid j 
(Three days only.) ) 


1.66 



The smaller amount of lactic acid seems to have produced as 
great an effect in reducing the proteid metabolism as an equal 
weight of dextrose, but no further effect was noted from an increase 
in its amount, as was the case with the dextrose. The acetic acid, 
on the contrary, seems to have had a tendency to increase rather 
than to diminish the proteid metabolism, and the same effect was 
indicated in one of the experiments on a rabbit. It is to be re- 
marked, however, that the sodium acetate appeared to be particu- 
larly obnoxious to the animals. In the case of the sheep it was in- 
troduced into the stomach in solution by means of a funnel, and 
besides causing the animal considerable discomfort had a very 
marked diuretic action. It may perhaps be questioned whether 
the results obtained under such conditions represent the normal 
effects of acetic acid. 

Pentose Carbohydrates. — While the fate of the pentose carbo- 
hydrates in the body has been the subject of considerable research 
(compare Chapter II, p. 24), their effect upon the proteid meta- 
bolism does not seem to have been specifically investigated, although 
Pfeiffer & Eber,f in the course of experiments upon the origin of 
hippuric acid, observed that after the consumption of 500 grams of 

* Assumed to be the same as with the basal ration. The actual nitrogen 
of the feces for these three days was 4.78 grms., making the apparently 
digested nitrogen 19.33 grms. 

\ Landw. Vers. Stat., 49, 137. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 125 

cherry gum, containing 41.98 per cent, of pentose carbohydrates, 
the urinary nitrogen of a horse decreased by over 6 per cent. They 
leave it uncertain, however, whether the effect was due to the 
pentosans or to other ingredients of the gum. 

Among the early experiments of Grouven * are also four in which 
gum arabic, added to an exclusive straw ration, materially reduced 
the proteid metabolism, but the methods of these early experiments 
were naturally somewhat defective. On the other hand, Cremer's 
experiments f with rhammose on rabbits showed no marked effect 
of this substance upon the proteid metabolism. 

Total A on-nitrogenous Matter of Feeding-stuffs. — The digestible 
non-nitrogenous matters of feeding-stuffs, aside from a small pro- 
portion of fat, are commonly although loosely grouped together as 
carbohydrates. They include both hexose and pentose carbohy- 
drates, such organic acids as may be present or as are formed during 
digestion, and a variety of other less well-known substances. 

As has already appeared in discussing the effect of crude fiber, the 
mixture of material included in the digestible crude fiber and nitro- 
gen-free extract shows the same tendency as starch and sugar to 
diminish the proteid metabolism. In other words, while the com- 
mon designation of digestible carbohydrates may be of questionable 
accuracy from a chemical point of view, nevertheless the some- 
what heterogeneous mixture to which it is applied behaves, in this 
respect at least, qualitatively like the pure hexose carbohydrates. 
Numerous instances of this are cited by v. Wolff | in his discus- 
sion of the data prior to 1876. Of more recent results, attention 
may be specially called to those of Kellner, some of which have 
been cited above. The results upon coarse fodders are those which 
are of particular interest, since it is these whose ingredients are 
least known chemically. They are presented on the following 
page in the same form as those upon extracted straw above. 

Although the addition of hay or straw to the basal ration in- 
creased the supply of digestible nitrogenous matter, the proteid 
metabolism was not proportionately increased, but in every instance 

* Wolff, Ernahrung Landw. Nutzthiere, p. 289. 

t Zeit. f. Biol., 42, 451. 

J Ernahrung Landw. Nutzthiere, pp. 288-309. 



126 



PRINCIPLES OF ANIMAL NUTRITION. 





-6 

o 

Ph 




Apparently Digested. 


Nitrogen 

of 

Urine. 




o 


"3 

■o 

3 
u 
O 


c 

•V 

a 
u 
O 


be g 
p u-S 


to fi 

= -h 

aj u m 

« ° s 


a 
a> 
be 
o 
g 

2 


Gain 

of 
Nitro- 
gen. 


F 
V 


1 
3 


Meadow Hay. 
Basal ration + hay . . 

il tl 

Difference 


Grnis. 

123 

90 


Grins. 
1553 
1007 


Grms. 
3850 
3014 


Grms. | Grms. 
1383 133.84 
1069 111.67 


Grms. 
97.19 
106.03 


Grms. 
36 . 65 
5.64 




33 


546 


836 


314 


22.17 


-8.84 


31.01 


G 


2 


Basal ration + hay . . 


58 


1675 


4006 


1498 108.96 


91.30 


17.66 


G 


3 


Difference 


20 


1137 


3120 


1143, 86.27 


86.30 


-0.03 




38 


538 


886 


355 ! 22.69 


5.00 


17.69 


11 
H 


2 

4 


Basal ration + hay . . 
a it 

Difference 


150 
101 


1786 
1083 


4037 
2912 


1487 i 145. 94 
1071 116.51 


122.19 
109.28 


23.75 

7.23 




49 


703 


1125 


416 29.43 


12.91 


16.52 


H 
H 


7 
4 


Basal ration + hay . . 

11 tt 

Difference 


165 
101 


1822 
1083 


4148 
2912 


1531)146.84 
1071416.51 


130.78 
109.28 


16.06 
7.23 




64 


739 


1236 


460 30.33 


21.50 


8.83 


J 
J 


2 

4 


Basal ration + hay . . 

it it 

Difference 


141 
107 


1797 
1114 


4108 
2895 


1542 
1059 


163.37 
128.11 


137.97 

122.62 


25.40 
5.49 




34 


683 


1213 


483 


35.26 


15.35 


19.91 






Oat Straw. 
















F 


2 


Basal ration + straw 


139 


1701 


3735 


1553 


119.15 


99.40 


19.75 


F 


3 


n tt 
Difference 


90 


1007 


3014 


1069 


111.67 


106.03 


5.64 




49 


694 


721 


484 


7.48 


-6.63 


14.11 


(; 


1 


Basal ration + straw 


86 


1732 


3804 


1574 


91.77 


71.36 


20.41 


c; 


3 




20 


1137 


3120 


1143 


86.27 


86.30 


-0.03 




66 


595 


684 


431 


5.50 


-14.94 


20.44 






Wheat Straw. 
















if 


1 


Basal ration + straw 


115 


1904 


3436 


1485 


110.80 


106.32 


4.48 


H 


4 


tt a 

Difference 


101 


1083 


2912 


1071 


116.51 


109.28 


7.23 




14 


821 


524 


414 


-5.71 


-2.96 


-2.75 


J 


1 


Basal ration + straw 


111 


1943 


3511 


1555 


128.94 


119.89 


9.05 


J 


4 


tt a 


107 


1114 


2895 


1059 


128.11 


122.62 


5.49 




4 


829 


616 


496 


0.83 


-2.73 


3.56 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 127 



save one the gain of nitrogen by the body showed a marked increase, 
and this, it is to be noted, after the feeding had been continued for 
a considerable time. The one exceptional case, on wheat straw, 
is readily explained by the obvious effect of this material in increas- 
ing the metabolic nitrogen of the feces and thus diminishing the 
apparent digestibility of the protein of the ration. Had account 
been taken of these metabolic products, the increased gain of 
nitrogen by the animals would doubtless have been more marked 
in all cases. This gain, it would seem, may fairly be ascribed to the 
large additions of digestible non-nitrogenous matter derived from 
the hay or straw added. 

Comparative Effects of Fat and Carbohydrates. — C. Voit * 
found the hexose carbohydrates to be superior to fat in diminishing 
the proteid metabolism. He gives the following comparisons: 



Date. 



Food per Day. 



Meat, 
Grms. 



Carbohydrates or Fat, 

Grms. 



Urea 

per Day, 

Grms. 



Nov. 16-22, 1857 

" 22-Dec. 2, 1857 

Oct. 28-Nov. 8, 1857 
Nov. 8-15, 

Feb. 23-25, 1861 

" 25-28 " 

" 28-Mch. 3, 1861 

June 19-23, 1859 

" 23-26, " 

" 26-29 " 

" 29-July 2, 1859 ! 



Feb. 17-22, 1865 . 
" 22-25, " . 



July 23-26, 1864 

" 26, " .... 

" 27, " ... 

" 27-Aug. 1, 1864 
Aug. 1, 1864 

" 2, " 

" 3, " 



Jan 7-12, 1859. 
" 12-15, " . 



150 
150 

176 
176 

400 
400 
400 

500 
500 
500 
500 

800 
800 

1000 
1000 
1000 
1000 
1000 
1000 
1000 

2000 
2000 



150-350 sugar 
250 fat 

100-364 starch 
250 fat 

200 fat 
250 starch 
250 sugar 

250 fat 
300 sugar 
200 " 
100 " 

250 starch 
200 fat 


100 starch 
400 " 


100 fat 
300 " 



200-300 starch 
250 fat 



13.4 
15.6 

15.1 
16.2 

31.9 
30.5 
30.3 

38.5 
32.7 
35.6 
37.9 

52.8 
54.7 

73.5 

68.5 
60.2 
79.6 
74.5 
69.3 
80.2 

128.4 
135.9 



* Zeit. f. Biol., 5, 447. 



J 28 PRINCIPLES OF ANIMAL NUTRITION. 

Subsequent investigations have substantially confirmed this 
conclusion. Thus Kayser * in an experiment upon himself found 
that the replacements of the carbohydrates of his diet by an amount 
of fat equivalent to them in heat value caused a marked increase 
in the urinary nitrogen, resulting in a loss of this element by the 
body in place of the previous small gain. The possible effect upon 
the apparent digestibility of the proteids of the food does not appear 
to have been considered. 

Wicke & Weiske f report two series of experiments upon sheep 
in which equivalent ("isodynamic") quantities of fat and of starch 
were added to a basal ration. In the first series the basal ration 
was comparatively poor in proteids and fat, having a nutritive ratio 
of about 1 : 8.3 ; in the second series it was richer in both these 
substances and had a nutritive ratio of 1 : 5.1 and 1 : 6.3 for the 
two animals respectively. As is usually the case, the starch dimin- 
ished the apparent digestibility of the protein of the basal ration, 
while the fat produced but a slight effect in this direction. Not- 
withstanding this complication, however, the effect of the starch 
in diminishing the proteid metabolism was clearly greater than 
that of the fat, and if the results were corrected for the increase 
in the nitrogenous metabolic products in the feces they would be 
still more decisive. 

The investigations of E. Voit & Korkunoff upon the minimum 
of proteids, which will be considered in a subsequent paragraph, 
also show a superiority in this respect of the carbohydrates over 
the fats which these authors ascribe to the greater lability of 
their molecular structure which enables them to enter into reactions 
in the body more readily than the fats. 

Magnitude and Duration of the Effect. — The pre-eminent 
position of the proteids in nutrition has perhaps led investigators 
to attach undue importance to this power of the non-nitrogenous 
nutrients to diminish the proteid metabolism. It is well to note 
that it is relatively small. C. Voit, as already stated, found an 
average decrease of about 7 per cent, with fats and about 9 per 
cent, with carbohydrates, and subsequent investigators have ob- 
tained results entirely comparable with these. 

Proteid Metabolism Determined by Supply. — In the presence 
*v. Noorden, Pathologie des Stoffwechsels, p. 117. 
fZeit. physiol. Chem., 21, 42; 22, 137. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 129 



ot non-nitrogenous nutrients it is still true that the proteid meta- 
bolism, or more exactly the excretion of nitrogen, is mainly deter- 
mined by the supply of it in the food just as it is upon an exclusive 
proteid diet. Fat or carbohydrates simply produce a relatively 
small, and probably more or less transitory, diminution of it with- 
out affecting the substantial truth of the above statement. 

Lawes & Gilbert,* in discussing the results of their fattening 
experiments upon sheep and pigs, called attention to the very wide 
variations in the amount of protein consumed, both per unit of 
weight and especially per unit of gain, and concluded that the ap- 
parent excess of protein in some cases must have served substan- 
tially for respiratory purposes. The subsequent investigations of 
Bischoff, Voit, and v. Pettenkofer upon the proteid metabolism of 
carnivora showed clearly that the dependence of the latter upon 
the proteid supply, which is so marked upon a purely proteid diet, 
is equally evident upon a mixed diet, and thus supplied a scientific 
explanation of the facts observed by Lawes & Gilbert. The 
effect of the proteid supply upon the nitrogen excretion is clearly 
shown by the following summary of Voit's experiments : f 



Food. 


Urea Excreted, 
Grms. 


Fat. 
Grms. 


Lean Meat. 
Grms. 


250 
300 
250 
200 
200 
250 


150 
176 
250 
500 
800 
1500 


17.0 
18.9 
19.7 
36.6 
56.7 
100.7 



Since Voit's researches, very many experiments, among the 
earliest of which were those of Henneberg & Stohmann J upon 
cattle, have confirmed his results, both for carnivora, herbivora 
and omnivora. A somewhat striking example is afforded by Stoh- 
mann's § experiments upon milch goats which are summarized in 
the following table : 

*Rep. Brit Asso. Adv. Sci., 1852; Rothamsted Memoirs, Vol. II. 

t Zeit. f. Biol , 5, 329. 

% Beitrage, etc., Heft 2, p 412. 

§Biologische Studien, 121. 



i3° 



PRINCIPLES OF ANIMAL NUTRITION. 



Date. 



Eaten per Day. 



Hay, 
Grms. 



Linseed 
Meal, 
Grms. 



Protein 

Digested 

per Day, 

Grms. 



Protein 

Metabolized 

per Day,* 

Grms. 



1 
2 
3 
4 
5 
6 
7 
8 
9 
10 



May 23-29 
June 6-12 

" 20-26 
July 4-10 

" 25-31 
Aug. 8-14 

" 22-28 
Sept 5-11 

" 19-25 
Oct. 3-9. 



1500 
1450 
1400 
1350 
1250 
1100 
950 
800 
1600 
1600 



100 
150 
200 
250 
350 
500 
650 
800 





111.6 
125.0 
132.2 
150.9 
170.5 
193.8 
221.4 
257.2 
92.9 
74.1 



66.6 

79.4 

90.6 

90.1 

101.6 

117.9 

143.1 

173.7 

56.3 

41.9 



A full compilation of these earlier results has been made by 
v. Wolff,f an d the fact is now so well established that further cita- 
tions would be superfluous. 

Rate of Nitrogen Excretion. — Some interesting hints as to 
the manner in which the non-nitrogenous nutrients produce the 
effect upon the proteid metabolism which has just been described 
are afforded by a consideration of the rate of nitrogen excretion 
under their influence. 

It was shown in the preceding section that the effect of a meal 
of proteids was a sudden, almost explosive, increase in the nitrogen 
cleavage and excretion, reaching its maximum within a few hours 
after the meal. If, however, non-nitrogenous nutrients are given 
along with the proteids, the character of the curve is essentially 
altered, the maximum rate of excretion being less and being reached 
somewhat later, while the fall from this maximum is less rapid. 
In other words, the rate of excretion becomes more uniform — the 
curve is flattened out. The influence of fat in this respect is clearly 
shown in the experiments of Panum J and of Feder J cited pre- 
viously, and appears evident also in those of Graff enberger. § In 
the latter experiments the nitrogenous substances to be tested were 
added to a mixed diet. The results show a distinct maximum, but 
the rate of decrease after the maximum was reached was not rapid, 

* Exclusive of the protein of the milk. 

t Ernahrung Landw. Nutzthiere, pp. 285-309 

J Thier. Chem. Ber., 12, 402. 

§Zeit. f. Biol., 28,318. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 131 

and only a part of the nitrogen appeared during the twenty-four 
hours following its ingestion, viz.: 

With fibrin 49 . 2 per cent. 

With gelatin 37.6 " " 

With peptone 67.6 " " 

With asparagin 79 . " " 

Rosemann's * results upon the rate of nitrogen excretion by 
man, likewise cited above, indicate a similar effect of the non- 
nitrogenous nutrients, the fluctuations due to the ingestion of mixed 
food being much less sharp than those found by other experi- 
menters with proteids alone. 

If we accept Rosemann's view (p. 101), that the sudden increase 
in the nitrogen cleavage is due, in part at least, to a direct stimulus 
to the metabolic activity of the cells, arising from the presence in 
the fluids of the body of an increased percentage of proteids, we 
may perhaps suppose that the simultaneous resorption of non- 
nitrogenous matter renders this stimulus less and so reduces the 
maximum rate of nitrogen cleavage. This conjecture possibly 
receives some support also from the results of Krummacher,f who, 
contrary to Adrian and Munk, finds that the division of the 
proteid ration into several meals not only renders the rate of nitro- 
gen excretion more uniform, but reduces somewhat the total amount 
excreted. Gebhardt J has also obtained similiar results. 

There is also the possibility, however, that the non-nitrogenous 
nutrients may modify the rate at which the proteids are resorbed, 
or perhaps, as has been suggested by various investigators, the 
extent to which the proteids are converted into amide-like bodies 
by the pancreatic juice or the extent of proteid putrefaction in the 
intestines. Suggestive in this regard is the fact found by Gruber § 
that common salt, which acts as a stimulant to the secretion of hydro- 
chloric acid by the stomach, and would thus tend to favor gastric 
as compared with intestinal digestion of the proteids, produces an 
effect on the nitrogen excretion similar to that of the non-nitroge- 
nous nutrients. 

*Arch. ges. Physiol., 65, 343. 
fZeit. f. Biol., 35, 481. 
J Arch. ges. Physiol., 65, 611. 
§ Zeit. f. Biol., 42, 425. 



I3 2 PRINCIPLES OF ANIMAL NUTRITION. 

Extent of Protein Storage. — Whatever may be the expla- 
nation of the action of the non-nitrogenous nutrients, its effect is 
obvious. Attention has already been called (p. 102) to Gruber's 
hypothesis that the transitory storage of nitrogen following an 
increase in the proteid supply is the result of a superposition of the 
daily curves of nitrogen excretion. The effect of the non-nitroge- 
nous nutrients appears to be to diminish the rate of nitrogen cleavage 
and to protract it, in the case of a single meal of proteids, over a 
longer time. Evidently, then, an increase of the proteid supply in- 
a mixed diet, or the addition of non-nitrogenous nutrients to a pro- 
teid diet, will extend its effect over a considerably longer period 
than in case of an exclusive proteid diet — that is, nitrogen equi- 
librium will be reached more slowly, and there will be a longer or 
shorter time after the change during which the nitrogen excretion 
will be less than in the absence of the non-nitrogenous matters. 

This explanation also implies, however, that the storage of 
nitrogenous matter in the body of the mature animal is of limited 
duration and that no long-continued gain of protein can occur; in 
other words, that it is impossible to materially increase the proteid 
tissue (lean meat) of a mature animal. 

Numerous comparative fattening experiments with domestic 
animals, notably those of Henneberg, Kern, & Wattenberg * upon 
sheep, fully sustain this conclusion. On the other hand, metabo- 
lism experiments with domestic animals rarely show an equality 
between the income of nitrogen and its outgo in feces and urine, 
but almost always indicate a gain of nitrogenous matter by the 
body. As regards the significance of this fact, however, several 
considerations must be borne in mind. 

First, the normal growth of the epidermal tissues — hair or wool, 
hoofs, horns, etc. — as pointed out in Chapter III, consumes a por- 
tion of the nitrogen of the food and contributes its share to the 
storage of nitrogen in the body. 

Second, the adipose tissue itself contains a small percentage of 
proteid matter, and a storage of fat in considerable amounts in- 
volves the production of new adipose tissue in which to store it. 

Third, in many cases the metabolism experiments which show 
a storage of nitrogen have been made within a rather short time 

*Jour. f. Landw., 26, 549. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 133 

after a change in the ration, and can therefore be interpreted as 
showing simply that sufficient time had not elapsed to reach nitro- 
gen equilibrium. 

If we consider also the somewhat indefinite nature of the term 
mature, and likewise the possibilities of error due to mechanical 
losses of excreta and to escape of nitrogen from the latter by fermen- 
tation and decomposition, we can readily see why the results of a 
short metabolism experiment may not agree with those of a long 
fattening experiment; yet, nevertheless, it must be confessed that 
the impression left by a comparison of the whole mass of evidence 
is that the discrepancy is as yet but partially explained. 

In conclusion, we may anticipate a discussion in Chapter VI, 
and call attention to the fact that muscular exertion may, to a 
limited extent at least, stimulate those constructive processes which 
result in a storage of protein in the body. 

The Minimum of Proteids. — In the preceding section it ap- 
peared that the administration of proteid food to a previously fast- 
ing animal caused a prompt and large increase in the nitrogen 
cleavage and excretion, while but a comparatively small portion 
of the proteids was applied to constructive purposes, the result 
being that two to three times as much proteids must be given as 
are metabolized during fasting before nitrogen equilibrium is 
reached. This effect was there ascribed to the stimulating effect 
of the rapid digestion and resorption of the proteids upon the nitro- 
gen cleavage, much of the proteids being apparently destroyed 
as such before they can serve for tissue-building. 

We have just seen that the effect of the non-nitrogenous nutri- 
ents is to diminish somewhat the nitrogen cleavage, apparently 
by moderating this stimulating effect. The necessary result is 
that, as the nitrogen supply is increased, it and the nitrogen excretion 
will start more nearly together and approach each other more rapidly 
upon a mixed diet than upon one consisting of proteids only. Conse- 
quently, while the percentage decrease in the proteid metabolism 
is, as we have seen, relatively small, nitrogen equilibrium may be 
reached with a much smaller supply of proteids than is the case in 
the absence of the non-nitrogenous nutrients. Indeed, it is con- 
ceivable that a sufficient supply of carbohydrates or fats in the diet 
should practically destroy the stimulative effects of the proteids in 



J 34 



PRINCIPLES OF ANIMAL NUTRITION. 



which case we might expect a proteid supply equal to the fasting 
proteid metabolism to be sufficient to produce nitrogen equilibrium. 
Seen in this light, the apparently insignificant effect of the non- 
nitrogenous nutrients becomes a very important factor in nutrition. 
The effect of the non-nitrogenous nutrients in largely diminish- 
ing the necessary proteid supply was pointed out by C. Voit * and 
appears clearly in many of his experimental results. Thus from the 
summary on p. 95 it appears that from 1200 to 1500 grams of lean 
meat per day was required to maintain the animal experimented 
upon in nitrogen equilibrium. When fat or carbohydrates were 
added to the ration, however, strikingly different results were 
reached, as appears from the following comparative statement, 
the results being expressed as " flesh " with 3.4 per cent, of nitrogen : 



Food. 



Meat. 



Fat or Carbo- 
hydrates. 



Flesh 
Meta- 
bolized. 



Gain of 
Flesh. 



Meat only (average of both series) . 



Meat and fat 



Meat and carbohydrates (compare 
p. 116) 



300 

600 

900 

1200 

1500 

500 

800 
1000 

500 

800 
1000 



250 
200 
250 

300-100 
100-400 
100-400 



416 

674 

943 

1207 

1478 

444 
720 
875 

502 
763 

902 



-116 

- 74 

- 43 

- 7 
+ 22 

+ 56 
+ 80 
+ 125 

- 2 
+ 37 

+ 88 



In the presence of non-nitrogenous nutrients, nitrogen equi- 
librium was reached with quantities of proteids from one third to 
one half as great as the amount required when fed alone. In other 
words, the non-nitrogenous nutrients materially reduced the mini- 
mum of food proteids required to maintain the proteid tissues of 
the body. 

In view of the peculiar importance of the proteids in nutri- 
tion, as well as of their relative scarcity and high cost, particu- 
larly in the food of our domestic animals, great interest attaches 
to a determination of the least amount required to sustain a mature 

* Zeit. f. Biol., 5. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 135 



.animal. The results obtained by E. Voit & Korkunoff * regard- 
ing the minimum requirement upon an exclusive proteid diet have 
already been stated in the first section of this chapter (p. 95). The 
same investigators have also studied the more interesting question 
of how far the necessary proteid supply can be reduced in the 
presence of non-nitrogenous nutrients. 

Proteids and Fat. — The experiments were upon the same 
general plan as those just referred to on proteids alone. Beginning 
with an insufficient quantity of proteids, the amount was gradually 
increased, that of the fat remaining constant, until nitrogen equi- 
librium was reached. As in those experiments, too, the nitrogen 
of the food was practically all in the proteid form, and its amount 
is compared with the proteid nitrogen excreted, it being assumed 
that 18.45 per cent, of the urinary nitrogen was derived from the 
extractives of the flesh metabolized in the body. To the writer it 
would seem that a more suitable unit would be the total excretory 
nitrogen, since the proteids of the food had to make good the loss 
of extractives as well as of true proteids from the body, and the 
former loss is as unavoidable as the latter. Accordingly, the results 
have been stated in the table below in both ways. 

Two series of experiments were made: one in which the total 
food-supply was less than was required to supply the estimated 
demands of the body for energy, and one in which it considerably 
exceeded that demand, with the following results: 



Series I: 

Experiment 1 
■ " 2 

Series II: 

Experiment 3 
4 



Total 

Excretion, 

Fasting, 

Grms. 



4.85 
4.22 



4.98 
4.01 
3.86 



Per Cent, of Energy 
Demand Supplied by 



Fat, 
Per Cent. 



72 
73 



116 

127 
137 



Total 

Food, 

Per Cent. 



90 
86 



128 
140 
150 



Minimum of Food Nitrogen. 



Amount, 
Grms. 



7.63 
>5.61 



>6.61 
5.12 

5.07 



Per Cent of Fasting 
Metabolism. 



Total, Proteid. 
Per Cent. Per Cent 



157 
>133 



>133 
128 
131 



193 
>163 



>162 
157 
161 



The authors also compute from experiments by C. Voit and by 
Rubner percentages lying between 162 and 207, and state as their 
* Zeit. f. Biol., 32, 58. 



136 PRINCIPLES OF ANIMAL NUTRITION. 

final result that the minimum of proteid nitrogen on a diet of pro- 
teids and fat lies between 160 and 200 per cent, of the proteid nitro- 
gen excreted during fasting. These figures when computed on the 
total excretory nitrogen would become 131 per cent, and 163 per 
cent, respectively. 

Proteids and Carbohydrates. — We have seen (p. 127) that 
the carbohydrates diminish the proteid metabolism to a greater 
extent than the fats. The results which have been reached as to 
their effect in lowering the minimum demand for proteids are on 
the whole in accord with this fact. With a liberal supply of carbo- 
hydrates in the food, a much smaller quantity of proteids would 
seem to suffice to maintain nitrogen equilibrium than when the 
non-nitrogenous matter of the ration consists of fat. Indeed, ac- 
cording to some investigators, the proteid metabolism may ever. 
be thus reduced much below that during fasting. 

Munk * appears to have been the first to advance the view last 
mentioned. In an investigation upon the formation of fat from 
carbohydrates a dog was fasted for thirty-one days and then re- 
ceived a diet consisting of a little meat with large amounts of 
carbohydrates (starch and sugar) and also, during the first twelve 
days, gelatin. Omitting these twelve days and also the earlier days 
of the fasting period, the average daily excretion of nitrogen in the 
urine was 

Twelfth to thirty-first days of fasting 5.38 grams 

Thirteenth to twenty-fourth days of feeding (200 

grams meat, 500 grams carbohydrates) 5.79 " 

On the seventeenth day of the feeding the urinary nitrogen 
reached the minimum of 4.133 grams, and Munk regards this as 
showing the possibility of a reduction of the proteid metabolism 
considerable below the fasting level. It is to be noted, however, 
that the nitrogen excretion varied considerably from day to day, 
and a selection of a single day for comparison seems hardly justified. 

Hirschfeld f and Kumagawa \ found that the nitrogen equili- 

* Arch. path. Anat. u. Physiol., 101, 91. 
t Ibid., 114, 301. 
% Ibid., 116, 370. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 137 

brium of man could be maintained on a diet containing little nitro- 
gen but abundance of non-nitrogenous nutrients. Under these 
conditions the urinary nitrogen was reduced to 5.87 grams and 6.07 
grams per day respectively, and the total nitrogen excretion to 
7.45 grams and 8.10 grams, amounts much lower than have been 
observed for fasting men. Thus in the extensive investigations by 
Lehmann, Milller, Munk, Senator, & Zuntz * of the metabolism 
of two fasting men, much higher figures than the above were ob- 
tained for the urinary nitrogen, and Munk (Joe. cit., p. 225) calls 
attention to the fact that in one case the urinary nitrogen on the 
second day succeeding the fasting period was materially less than 
on the last day of the fasting, viz., 8.26 grams as compared with 
9.88 grams. 

In a subsequent series of experiments upon dogs, Munk f showed 
that by very liberal feeding with food poor in proteids (rice with 
small amounts of meat) the nitrogen balance could be maintained 
for a considerable time at an amount very much lower than pre- 
vious observers had found for the proteid metabolism of fasting 
dogs of similar weight. 





Length 
of Exper- 
iment, 
Days. 


Average 
Live 

Weight, 
Kgs. 


Food per Day. 


Urinary 




Fat, 
Grms. 


Starch, 
Grms. 


Nitrogen, 
Grms. 


Nitro- 
gen, 
Grms. 


[h 1 

With food: < ^ 

I IV 

-p ,. (Munk 

Fasting: | Falck 


5 
5 
4 
4 


11.20 
10.21 

9.88 
8.25 

14.4 

8.9 


55 
38 
53 
47 


116 

96 

108 

100 


2.63 

2.48 
2.66 
2.60 


2.61 
2.40 
2.67 
2.62 

3.65 
5.10 



Munk also cites in support of his conclusions Rubner's results 
on a dog fed exclusively on carbohydrates. A reference to these 
results as tabulated on a subsequent page does in fact show in most 
cases a decrease in the proteid metabolism as compared with the 
fasting values, but how much of this is due to the normal decrease 
during the first few days of abstinence from proteid food it is dif- 

*Arch. path. Anat. u. Physiol., 131, Supp. 
jlbid., 132,91. 



138 



PRINCIPLES OF ANIMAL NUTRITION. 



ficult to decide. Munk also cites results obtained by Salkowski,* 
who observed the nitrogen excretion of a dog on a light ration con- 
taining but little proteids to be scarcely greater than in the absence 
of all food. 

E. Voit & Korkunoff (loc. cit.) also included the carbohydrates 
in their investigation upon this subject, following the same general 
method as in the experiments with fat. The following are their 
results compared with the fasting proteid metabolism exactly as 
in the former case: 









Per Cent, of 


Minimum 


of Food Nitrogen. 






Total 


Energy Demand 














Live 


Nitrogen 


Supplied by 




Per Cent.of Fasting 




Weight, 
Kgs. 


Excre- 






JVlt^tiibolism 




tion, 
Fasting, 


Carbo- 


Total 
Food, 


Amount, 
Grms. 














Grms. 


hydrates, 


Per 




Total, 


Proteid, 








Per Cent. 


Cent. 




Per Cent. 


PerCent. 


Series I: 












t 


Experiment 3a 


24.0 


4.93 


78 


91 


>5.43 


>1!0 1 >133 


2 


24.6 


4.94 


79 


92 


5.00 


101 


124 


Series II: 
















Experiment 5 


27.7 


4.98 


111 


122 


5.11 


103 


126 


1 


24.1 


5.25 


115 


126 


>4.91 


>94 


>123 


2 


24.7 


4.94 


118 


131 


<4.35 


<88 


<108 


4 


30.0 


4.08 


122 


136 


<4.47 


<110 


<134 


36 


24.0 


4.93 


155 


168 


<4.48 


<91 


<111 



The authors also compute from a few experiments by C. Voit 
and by Rubner values not inconsistent with the above. 

When compared with the total nitrogen excretion, the results of 
Voit & Korkunoff show in but a single case a minimum unmistak- 
ably greater than the fasting proteid metabolism. In three cases 
the minimum falls below this amount, while in the remaining cases 
it is either substantially equal to it or doubtful. Regarded in this 
way, they seem on the whole in accord with Munk's claim that the 
proteid metabolism may be reduced below the fasting limit. Voit 
& Korkunoff, however, dispute this and subject Munk's experi- 
ments to a detailed criticism, the principal points of which are that 
in the earlier experiments, as noted above, the nitrogen excre- 
tion was irregular and that the result of a single day is arbi- 
trarily selected for comparison, while in the later experiments no 
* Zeit. physiol. Chem., 1, 44. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 139 

determinations of the fasting metabolism of the animals actually 
used for the experiments were made. By a re-computation of 
Munk's experiments they obtain results varying but little from 
100 per cent. A computation from the average figures given on 
p. 136, assuming 3.4 per cent, of nitrogen in the meat and 0.51 
grams of nitrogen per day in the feces, shows that the minimum is 
probably less than 107 per cent, of the fasting nitrogen excretion. 

Much depends, however, upon whether we take as the unit of 
comparison the total nitrogen excretion or, like Voit & Korkunoff, 
eliminate that portion derived from the extractives. If we select 
the former, then it appears that with a liberal supply of carbohy- 
drates in the food the supply of proteids certainly need not exceed 
the fasting metabolism in order to maintain nitrogen equilibrium, 
and perhaps may be reduced materially below it. 

Finally, it must be remembered that the fasting proteid meta- 
bolism itself is not a constant. In Chapter IV it was shown that 
as the store of fat in the body of a fasting animal becomes depleted 
the body proteids are drawn upon to an increasing extent to supply 
energy to the animal. It is not possible to show that the experi- 
mental results which have been cited are materially affected by this 
variability of the fasting proteid metabolism — indeed, it seems 
doubtful whether they are—but the fact that the demands of the 
organism for energy may affect the proteid metabolism is of itself 
sufficient to show that our unit of comparison, while practically 
convenient and perhaps sufficiently accurate, is not invariable. 

Amount of Non-nitrogenous Nutrients Required. — In 
most of the experiments which have been cited, the very low figures 
for the necessary proteid supply have been obtained by the em- 
ployment of an amount of non-nitrogenous nutrients materially 
in excess of the estimated requirements of the animal for energy, 
although in no case was this latter factor actually determined. 

Siven,* however, experimenting upon himself with a diet equal 
in amount to that ordinarily required to maintain his weight, was 
able to gradually reduce the total nitrogen of his food to 4.52 grams 
and maintain nitrogen equilibrium. He did not determine his fast- 
ing metabolism, but the above figure, which is equivalent to 0.08 
gram of nitrogen per kilogram live weight, is lower than the low- 
* Skand. Arch. f. Physiol., 10, 91. 



140 



PRINCIPLES OF ANIMAL NUTRITION. 



est fasting values previously obtained, Moreover, much of the 
nitrogen of his food was in the non-proteid form, the proteid nitro- 
gen being estimated at only 0.03 gram per kilogram live weight. 

Cremer & Henderson * have attempted to reproduce Siven's 
results in two experiments upon a dog, the total amount of food 
being equal to or slightly less than the estimated requirements of 
the animal. Under these conditions they were unable to reach 
even as low a minimum as did Voit & Korkunoff . On the other 
hand, Jaffa, t in a dietary study of a child on a diet of fruits and nuts 
(so-called frutarian diet), observed a gain of nitrogen by the sub- 
ject with only 0.041 gram of food nitrogen per kilogram body weight. 

The Minimum for Herbivora. — The ordinary food of our 
domestic herbivora contains an abundance of non-nitrogenous 
matter and relatively little protein. It is impossible, for obvious 
reasons, to determine the fasting metabolism of ruminants, and 
the basis for comparisons like those made above is therefore 
largely lacking. There is, however, abundant evidence to show that 
only a comparatively small amount of proteids is necessary to 
maintain the nitrogen equilibrium of cattle in particular, although 
exact data as to the least amount required are still lacking. 

The early experiments of Henneberg & Stohmann J upon the 
maintenance ration of cattle furnish the following examples of the 
sufficiency of a very small proteid supply, the results being com- 
puted per 500 kgs. live weight per day : 





Digested. 


Gain of 




Protein, 
Grnis. 


Non-nitrogenous 

Nutrients, 

Grms. 


Nitrogen 

by Animal, 

Grms. 


Ox I: 


178 
259 
209 

278 


4247 
3546 
3926 

3607 


4.0 


" 2 


21.0 


" 3 


11.0 


Ox II: 

Period 2 


19.5 







* Zeit. f. Biol., 42, 612. 

t U. S. Dept Agr., Office of Expt. Stations, Bull. 107, 21. 
J Beitriige zur Begrundung einer rationellen Futterung der Wiederkauer, 
Heft I. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 141 



The following figures, obtained by the same investigators * in 
later experiments, are taken from Wolff's compilation : f 





Live 

Weight, 

Kgs. 


Digested. 


Gain of 




Protein, 
Grms. 


Non-nitrogenous 

Nutrients, 

Grrns. 


Nitrogen 

by Animal, 

Grms. 


1860-61. 
Ox I. Period 5 


514 
531 
533 
625 
643 

638 
643 
661 
701 

715 


315 
405 
375 
280 
435 

395 
410 

400 
445 
390 


2435 
4090 
4980 
3060 
4590 

4995 
3610 
3620 
5540 
6060 





" 14 

" 16 

Ox II. Period 6 


+ 9.6 
+ 24.8 
+ 9.6 
+ 14 4 


" 15 


1865. 

Ox I. Experiment 1 

2 

3 

Ox II. " 5 

6 


+ 0.5 

- 0.8 
+ 4.0 

- 6.4 
+ 3.2 



G. Kiihn's extensive investigations at Mockern.J together with 
subsequent ones by Kellner,§ afford the following data for the 
periods in which the ration was approximately a maintenance 
ration : 





Live 

Weight, 

Kgs. 


In Digested Food. 


Gain of 




Protein, 
Grms. 


Metabolizable 

Energy, 

Cals. 


Nitrogen 

by Animal, 

Grms. 


Kiihn's Experiments: 

Ox II. Period 1 


632 
632 
631 
623 
602 
644 
672 

620 
612 

748 
750 
858 


413 
338 
339 
320 
451 
458 
540 

440 
213 
343 
696 
665 


16388 

17986 
18077 
17125 
15072 
15872 
17416 

16322 
15447 
13716 
18655 
24558 


+ 0.1 


" III. " 1 


- 2.6 


" IV. " la 


- 0.5 


" IV. " 16... 


- 5 7 


" V. " 1 


+ 8.5 


" VI. " 1 


+ 6.3 


" XX. " 1 


+ 3.3 


Kellner's Experiments: 

Ox A 


+ 6.2 


" B 

" I 


-14.6 
-13.8 


1 — 1 1 — 
1 — 1 1 — 1 

1— 1 


- 2.8 
+ 5.1 







* Beitrage, etc., Heft II., and Neue Beitrage, etc. 
t Erniihrung landw. Nutzthiere, pp. 406-410. 
j Landw. Vers. Stat., 44, 257. 
§Ibid., 47, 275; 50, 245. 



142 



PRINCIPLES OF ANIMAL NUTRITION. 



Experiments by the writer * have shown that nitrogen equi- 
librium may be maintained, for a time at least, on even smaller 
amounts of protein than the above figures would indicate. The 
figures in the first column of the following table signify the proteid 
nitrogen only of the food multiplied by 6.25 : 





Digested Pro- 
teids per Day 
and 500 Kgs. 
Live Weight, 
Grms. 


Meta- 
bolizable 

Energy 

of Food, 

Cals. 


Average 
Live 

Weight, 
Kgs. 


Gain or Loss 

of Nitrogen 

by Body, 

Grms. 


Nutritive 

Ratio 

1: . 


Experiment I: 

Steer 1 


129 
113 
133 

192 

202 
209 

297 
277 
314 

156 
131 
152 

258 
242 
275 


7956 
7588 
7191 

8144 
9590 
8084 

11130 
11318 
11324 

11955 
11904 
11557 

11634 
12976 
12030 


420 
450 
400 

420 
450 
400 

450 
490 
430 

450 
490 
430 

543 
629 
516 


-2.51 
-0.39 
-1.08 

+ 1.76 
+ 4.23 
+ 4.62 

+ 4.67 
+ 6.47 
+ 2.65 

+ 5.68 
+ 3.98 
+ 4.15 

+ 0.26 
-0.20 
-2.31 


20.1 


" 2 


20.4 


" 3 


18.6 


Experiment II: 
Steer 1 


13.4 


" 2 


13.6 


" 3 


12.8 


Experiment VI: 
Steer 1 


10.9 


" 2 


10.9 


" 3 


10.6 


Experiment VII: 
Steer 1 


23.0 


" 2 


25.3 


" 3 


23.9 


Experiment VIII: 
Steer 1 


10.4 


" 2 


10.7 


" 3 


10.6 



While the above data are hardly sufficient to fix absolutely the 
minimum of proteids for cattle on a maintenance ration, they indi- 
cate clearly that from 200 to 300 grams of digestible protein per day 
is at least sufficient for a steer weighing 500 kgs., and there is a 
possibility that the amount may be somewhat further reduced. 
Although we are unable to compare this with the fasting meta- 
bolism, a comparison on the basis of live weight with some of the 
results previously cited shows that the minimum demand for pro- 
teids on the part of cattle is relatively much less than on the part 
of carnivora. Thus the results obtained by Lehmann et. al. and 
Munk (p. 137), and by Voit & Korkunoff (p. 138), computed in 
*Penna. Expt. Station, Bull. 42, 165. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 143 



grams of food nitrogen per kilogram live weight, give the following 
figures for the minimum nitrogen requirements of the dog and of 
man as compared with cattle : 



Experiments on Dogs. 



Munk 



0.235 gram. 
0.243 " 
0.269 " 
0.315 " 



Average. 



Voit & Korkunoff . 



Experiments on Man. 



Lehmann et al . 



0.266 

f >0.226 
0.203 
0.185 
>0.204 
<0.176 
<0.149 
<0.187 



0.190 
0.180 
0.090 
0.180 



Experiments on Cattle. 
Range of experiments cited . 064-0 . 098 gram. 

Only one of the results on man, together with the very low 
figure obtained by Siven (p. 139), is comparable with those reached 
with cattle. Whether we are to ascribe the small demand of the 
latter for proteids to a specific difference in their rate of meta- 
bolism or to the large amounts of carbohydrate material which 
they habitually consume does not clearly appear. 

Effects upon Health. — Munk, in his experiments with rations 
very poor in proteids, made the observation that while such rations 
were adequate to .maintain the nitrogen balance of the body they 
nevertheless appeared to produce, in time, profound functional dis- 
turbances, sometimes ending in death. Similar observations have 
also been made by Rosenheim.* These experimenters ascribe 

*Arch. ges. Physiol., 54, 61. 



144 



PRINCIPLES OF ANIMAL NUTRITION. 



the ill effects directly to the small supply of proteids, but some other 
writers appear inclined to explain them as due to the long continu- 
ance of a uniform and rather artificial diet. The writer's experi- 
ments, cited above, showed no evidence of any ill effect in the case of 
cattle upon a ration containing but about 200 grams digestible pro- 
tein per day and continued for seventy days, and subsequent obser- 
vations, as well as the common experience of farmers in wintering 
cattle upon such feeding-stuffs as inferior hay, straw, etc., fully 
confirm this result. 

Effects on Total Metabolism. 

Substitution for Body Fat.— We have seen in the preceding 
section that proteid food, or rather the non-nitrogenous residue 
arising from its cleavage in the body, may be utilized as a source of 
energy in place of the body fat which would otherwise be meta- 
bolized. Similarly, the non-nitrogenous nutrients supplied in the 
food may be thus substituted for body fat in the metabolism of the 
animal. The substitution is shown most clearly in experiments 
upon fasting animals, although it appears also in those in which 
these nutrients are added to an insufficient ration. 

Fat. — The following averages of Pettenkofer & Voit's experi- 
ments,* computed from Atwater & Langworthy's digest,! illustrate 
this substitution of food fat for body fat : 



Food, 
Grms. 


Number of 
Experiments. 


Gain or Loss by Body. 


Nitrogen, 
Grms. 


Fat, 
Grms. 


Nothing 
100 fat 
350 " 


5 
2 
1 


-6.64 
-4.90 

-7.70 


- 97.76 

- 16.25 
+ 113.60 



The smaller amount of fat not only diminished the proteid meta- 
bolism but also largely reduced the loss of fat from the body. The 
larger amount of fat showed the tendency noted on p. 115 to increase 
the proteid metabolism, but at the same time it not only suspended 
the loss of body fat but caused a storage of fat in the organism. Of 
course we have no means of distinguishing in such a case between 

* Zeit. f. Biol., 5, 370. 

f U. S. Dept. Agr., Office of Experiment Stations, Bull. 45. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 145 

food fat and body fat, but it is most natural to suppose that the re- 
sorbed fat of the food, being already in circulation in the body, is 
more easily accessible to the active cells than the stored-up fat of 
the adipose tissue and is, therefore, metabolized in preference to the 
latter. 

Rubner,* in his study of the replacement values of the several 
nutrients, has demonstrated the same effect of food fat. Fat 
supplied in the food is utilized as a source of energy to the body and 
a corresponding quantity of body fat escapes oxidation, while if 
supplied in excess fat is stored up in the body. The experiments 
were made in the same manner and are. computed on the same 
assumptions as those upon proteids recorded on p. 106. All were 
on dogs except the third, which was on a rabbit. 



Food. 



Total Nitrogen 

of Excreta, 

Grms. 



Fat 

Metabolized, 

Grms. 



Gain or Loss 
of Fat, 
Grms. 



Nothing 

200 grms. bacon 

Nothing 

39 . 75 grms. of butter fat 

Nothing , 

26 . 1 grms. bacon j 

Nothing 

100 grms. fat 

Nothing 

40 grms. bacon 



1.69 
1.68 

2.14 
2.44 

0.778 
1.045 

2.56 
2.48 

1.08 
1.32 



60.47 
71.80 

33.78 
33.48 

7.18 
6.44 

42.40 

47.73 

22.88 
28.73 



- 60.47 
+ 128.20 

- 33.78 
+ 6.27 

- 7.18 
+ 19.63 

- 42.40 
+ 52.27 

- 22.88 
+ 11.27 



In nearly every case there was a slight increase in the proteid 
metabolism, as in Pettenkofer & Voit's experiments, and a some- 
what greater, although still not very considerable, increase in the 
fat metabolism. In the main, however, the food fat was metabolized 
in place of the body fat. 

In those of Pettenkofer & Voit's experiments in which fat was 
added to an insufficient ration of meat the same effect was pro- 
duced, as appears when we compare the results upon a ration of meat 

* Zeit. f. Biol., 19, 328-334; 30, 123. 
t Results approximate only. 



146 



PRINCIPLES OF ANIMAL NUTRITION. 



and fat given on p. 150 with those upon the same ration of meat 
without the fat, as in the table below: 





Number 

of 
Experi- 
ments. 


Food per Day. 


Gain or Loss by Body. 




Meat, 
Grms. 


Fat, 
Grms. 


Nitrogen, 
Grms. 


Carbon, 
Grms. 


" and fat 


6 
1 
5 


500 
500 
500 


ioo 

200 


-3.4 

+ 0.3 
-0.6 


-49.1 
+ 27.1 


a tt 11 


+ 67.3 







Carbohydrates. — The more soluble hexose carbohydrates 
when given to a fasting animal serve, like the fats, as a source of 
energy for the organism in place of the body fat which would other- 
wise be oxidized. 

The following is a summary of the average results obtained by 
Pettenkofer & Voit * by feeding starch with a small amount of 
fat, the fasting metabolism being the same as that just given on 
p. 144, The averages are computed as before from Atwater & 
Langworthy's digest (loc. cit.): 





Number 

of 
Experi- 
ments. 


Food per Day. 


Gain or Loss by Body. 




Starch, 
Grms. 


Fat, 
Grms. 


Nitrogen, 
Grms. 


Carbon, 
Grms. 


Fasting 


5 

11 


450 
597 
700 


lrj'9 
21.2 
20.2 


-6.64 
-7.20 
-9.40 
-6.20 


-97 76 


Starch 


+ 19.40 
-28.50 




+ 61.30 



The fasting metabolism in this case represents a series of experi- 
ments antedating by a year or two that upon starch. In only one 
case were the respiratory products of the fasting animal determined 
during the latter series. That determination immediately fol- 
lowed a day on which a large amount of starch was consumed, 
and the results are believed by the authors to be affected thereby. 
No very strict comparison is therefore possible, but the general 
effect of the starch in diminishing the loss of body fat is evident. 

*Zeit. f. Biol., 9, 485. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 147 

The experiments by Rubner,* which have been already several 
times referred to, include trials in which sugar or starch was fed 
alone. The results are computed as previously described, with the 
additional assumption that all the carbohydrates digested (with the 
exception of small amounts of sugar found in the urine in some 
cases) were completely oxidized in the body. The gain or loss of 
carbon as fat is therefore computed by subtracting from the total 
excretory carbon, first, the carbon due to the protein metabolized, 
and second, that assumed to be derived from the carbohydrates. 
On this basis the results are as follows, the amounts of carbohydrates 
given in the table being those believed to have been actually oxi- 
dized : 



Food. 



Total Nitrogen 

of Excreta, 

Grms. 



Total Carbon 

of Excreta,+ 

Grms. 



Gain or Loss 
of Fat, 
Grms 



Nothing 

76 . 12 grms. cane-sugar 
104.97 " " " 

Nothing 

97 . 3 grms. cane-sugar . 

17.0 " " " . 

143.0 " " " . 

Nothing 

34 grms. cane-sugar .... 
45 " " " .... 

50 " " " 

Nothing 

Nothing 

42 . 96 grms. starch 

Nothing 

57 . 38 grms. starch 

Nothing (second day) . . . 
94 . 36 grms. cane-sugar 
67.96 " starch 
4.70 " fat 



1.94 
1.45 
1.07 

1.86 
1.92 
1.41 
1.22 

1.32 
1.41 
1.25 
1.57 
1.39 



42 
53 



2.00 
1.52 

2.64 

1.23 



38.18 
43.19 

47.78 

39.22 
50.69 
39.52 
46.45 

21.36 
26.18 
29.14 
27.68 
25.79 

26.47 
33.28 

31.53 
39.67 

27.86 

38.94 



- 40.99 

- 8.41 
+ 0.51 

- 42.72 

- 2.95 

- 35.80 
+ 23.32 

- 21.88 

- 9.10 

- 7.46 

- 1.64 

- 27.86 

- 28.10 

- 10.54 

- 32.10 

- 10.74 

- 24.97 
+ 116.351 



In place of the slight increase in the proteid metabolism fre- 
quently noticed when fat is consumed, the tendency of the carbo- 

*Zeit. f. Biol., 19, 357-379; 22, 273. 

fNot including the carbon of the carbohydrates found in feces and urine. 

J Total gain of carbon, computed as fat. Compare, loc. cit., 22, 279. 



PRINCIPLES OF ANIMAL NUTRITION. 



hydrates seems to be to cause a slight decrease, but the chief effect 
is upon the carbon metabolism, increasing rations of carbohydrates 
resulting in a progressive reduction of the amount of body fat meta- 
bolized. 

The effect of starch or sugar when added to an insufficient pro- 
teid diet may be illustrated, as in the case of fat, by a comparison 
of Pettenkofer & Voit's results, cited on p. 150, with those on pro- 
teids alone: 





Number 

of 
Experi- 
ments. 


Food per Day. 


Gain or Loss 
by Body. 




Meat, 
Grms. 


Fat, 
Grms. 


Starch, 
Grms. 


Dextrose, 
Grms. 


Nitrogen, 
Grms. 


Carbon, 
Grms. 


Proteids alone 

" and starch . . . 
" " dextrose . 


6 

8 
3 


500 
500 
500 


5~3 


200 


200 


-3.4 
-1.8 
-1.3 


-49.1 
+ 9.0 

+ 7.2 



Mutual Replacement of Nutrients. — The facts which have been 
considered in the foregoing pages show a remarkable degree of 
flexibility in the animal organism as regards the nature of the mate- 
rial consumed in its vital processes. The amount of proteid mate- 
rial necessarily required for the metabolism of the mature animal 
we have seen to be relatively small. Aside from this minimum, the 
metabolic activities of the body may be supported, now at the ex- 
pense of the stored body fat, now by the body proteids, and again 
by the proteids, the fats, or the carbohydrates of the food. What- 
ever may be true economically, physiologically the welfare of the 
mature animal is not conditioned upon any fixed relation between 
the classes of nutrients in its food-supply, apart from the minimum 
requirement for proteids. The possibility of a mutual replacement 
of the several classes of nutrients in the food follows almost neces- 
sarily from the power of the organism to utilize them all indiffer- 
ently (in a qualitative sense at least). 

Replacement of Proteids. — It has been shown that proteids 
in excess of the minimum demand can be used by the organism to 
take the place of body fat previously metabolized. Furthermore, 
as we have just seen, the non-nitrogenous nutrients of the food may 
likewise be substituted for body fat. It is natural to suppose, there- 
fore, that that portion of the proteid supply which serves substan- 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 149 

tially as a source of energy only may be replaced either by body fat 
or by other food nutrients, and this supposition is borne out by the 
observed facts. 

By Body Fat. — In considering the total metabolism of the fast- 
ing animal in Chapter IV, we saw that the fat of the body has a 
marked effect in protecting the body proteids from metabolism, and 
that with the progressive impoverishment of the body in fat, more 
and more of the proteids are substituted for the latter as a source of 
energy. In § 1 of the present chapter it was further shown that 
the food proteids, or their non-nitrogenous residue, may be oxi- 
dized in the organism in place of the stored fat of the body. 

It is clear, however, that the same experiments may equally 
well be regarded from the converse point of view as showing that 
the body fat may be oxidized and serve as a source of energy in 
place of the proteids of the food or of the body. In other words, 
it is possible, within quite wide limits, for the animal organism to 
draw its supply of energy, according to circumstances, either from 
food or body proteids or from its stored-up fat. 

By Fats and Carbohydrates of Food.- — When, in addition to its 
reserve of fat, a supply of non-nitrogenous nutrients is afforded in 
its food, this range of choice by the organism is still further widened. 
In considering the effects of non-nitrogenous nutrients upon the 
proteid metabolism, and particularly in the discussion of the mini- 
mum of proteids, it became evident incidentally that fat or car- 
bohydrates may to a large extent be substituted for proteids in 
the food. A certain minimum of proteids was shown to be essential 
to the maintenance of the proteid tissues of the body, but proteids 
supplied in excess of this amount undergo nitrogen cleavage and 
serve substantially as a source of energy. This excess of proteids, 
as we have seen, can be replaced in the food by non-nitrogenous 
nutrients, particularly the carbohydrates, at least without damage 
to the proteid nutrition, as is shown by Voit's results there 
cited (p. 134). The later respiration experiments of Pettenkofer 
& Voit show that this is true also as regards the total metab- 
olism. As appears from the table on p. 109, a ration of 1500 
grams of lean meat sufficed to maintain the dog experimented 
upon approximately in equilibrium as regards the income and 
outgo of both nitrogen and carbon. When, however, a con- 



i5° 



PRINCIPLES OF ANIMAL NUTRITION. 



siderable proportion of this meat was replaced by fat, starch, or 
sugar, not only was the nitrogen equilibrium maintained but the 
same was true of the carbon, as appears from the following averages 
computed from Atwater & Langworthy's " Digest of Metabolism 
Experiments." * The results of Pettenkofer & Voit's first series 
with 1500 grams of lean meat as given by them are also included 
in the table: 





Food per Day. 


Gain or Loss 
by Body. 




Meat, 
Grms. 


Fat, 
Grms. 


Starch, 
Grms. 


Grape- 
sugar, 
Grms. 


Nitrogen, 
Grms. 


Carbon, 
Grms. 


Proteids only: 

Series I 


1500 
1500 

500 
500 

500 
500 


100 
200 

5.3 


200 


200 



+ 0.6 

+ 0.3 
-0.6 

-1.8 
-1.3 


+ 3.3 


Average of all (22 experiments) 

Proteids and fat : 

100 grms. fat (1 experiment) . . 
200 " " (5 experiments) . 

Proteids and carbohydrates : 

Starch (8 experiments) 

Grape-sugar (3 experiments) . . 


+ 8.7 

+ 27.1 
+ 67.3 

+ 9.0 
+ 7.2 



While it is true, as was stated on page 109, that there is reason 
to suppose the carbon balance as computed by Pettenkofer & 
Voit to be somewhat in error, this in no way affects the general 
showing of the above averages. The introduction into the diet of 
100-200 grams of fat or carbohydrates made it possible to dispense 
with two thirds of the proteids previously required to maintain the 
animal, the remaining 500 grams of meat being nearly or quite suffi- 
cient to maintain nitrogen equilibrium. The fat or carbohydrates 
added were obviously used by the organism as sources of energy in 
place of the proteids (or their non-nitrogenous residue) oxidized 
for this purpose on a purely proteid diet, since the stored fat of the 
body was not only conserved but even shows a gain. 

Rubner's investigations upon the source of animal heat t afford 



* U. S. Dept. Agr., Office of Expt. Stations, Bull. 45. 
Biol., 7, 450-480; 9, 6-13 and 450-467. 
t Zeit. f. Biol., 30, 125-132. 



Compare Zeit. f. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 15 1 

a similar illustration of this effect of non-nitrogenous nutrients. 
Assuming average figures for the nitrogen and carbon content of the 
food materials used, he obtained the following results : 





Food per Day. 


Gain or Loss by Body. 




Meat, 
Grms. 


Fat, 
Grms. 


Nitrogen, 
Grms. 


Carbon, 
Grms. 


Proteids alone (1 experiment) 

" and fat (2 experiments). . . . 


350 

80 


30 


+ 1.66 
-0.08 


-2.69 
+ 4.46 



The possibility of such a substitution of non-nitrogenous nutri- 
ents for the food proteids as is illustrated in the foregoing experi- 
ments seems, indeed, almost a necessary corollary of the facts con- 
cerning proteid metabolism considered on previous pages. We 
have seen that, beginning with the fasting metabolism, the effect 
of successive additions of proteids to the food is to stimulate the 
proteid metabolism. Only a relatively small proportion of the 
added proteids is employed by the organism for constructive pur- 
poses, the larger part of it undergoing very promptly nitrogen 
cleavage and thus constituting, to all intents and purposes, an ad- 
dition to the supply of non-nitrogenous material available for 
metabolism. It appears quite natural, then, that the portion of 
the proteid supply which thus serves substantially as fuel to the 
organism should be replaceable in the food by non-nitrogenous 
materials which are capable of serving the same purpose. 

Fats and Carbohydrates.— The apparent identity of the func- 
tions of the fats and carbohydrates as sources of energy which has 
been shown in the preceding paragraphs necessarily implies the 
possibility of their mutual replacement in the food. Rubner * has 
completed the chain of evidence by showing experimentally that fat 
and dextrose may thus replace each other. A dog received for 
twelve days a ration of 300 grams of lean meat and 42 or 50 grams 
of fat, with the exception of three days, on which varying amounts 
of dextrose were substituted for the fat. On six days the respi- 
ratory products were determined. Averaging the results for all 
the days on which the food was the same, and assuming the lean 

* Zeit. f. Biol., 19, 370. 



152 



PRINCIPLES OF ANIMAL NUTRITION. 



meat used to have contained 3.4 per cent, of nitrogen and 12.51 
per cent, of carbon, and the fat 76.5 per cent, of carbon, we have: 





Food per Day. 


Gain or Loss by Animal, 




Meat, 
Grms. 


Fat, 
Grms. 


Dextrose, 

Grms. 


Nitrogen, 
Grms. 


Carbon, 

Grms. 


Meat and fat 


\ 300 
|300 
(300 
,'300 
(300 


42 
50 


63.7 

79.7 
115.5 


+ 1.81 
+ 0.10 

+ 1.78 
+ 2.28 
+ 1.98 


+ 1.27 


Meat and dextrose .... 


+ 9.31 
-7.44 
-8.15 
+ 6.21 



The averages of Pettenkofer & Voit's results as tabulated on 
p. 150 may likewise be regarded in this light. 

Relative Values. — The close similarity in the functions of the 
several non-nitrogenous nutrients is too obvious to have escaped 
early notice, and the investigations of the Munich school of physi- 
ologists served both to emphasize the similarity and to follow it 
into details. To Rubner, a pupil of Voit, is generally ascribed 
the credit of having first placed in a clear light the quantitative 
relations of the subject, although v. Hosslin * and Danilewsky f 
enunciated similar ideas at about the same time, which, however, 
were not based on their own experiments. 

As the result of his investigations upon the replacement values 
of the nutrients,| Rubner announced the law of "isodynamic re- 
placement." This law is, in brief, that the several nutrients can 
replace each other in amounts inversely proportional to their physi- 
ological heat values, that is, to the amounts of heat which they 
would liberate if oxidized to the same final products which 
result from their metabolism in the body. In other words, aside 
from the minimum of proteids the nutrients are of value to the 
organism in proportion to the amount of energy which their meta- 
bolism liberates— they are " the fuel of the body." One gram of 
fat, for example, when oxidized to carbon dioxide and water, liber- 
ates about 9.5 Cals. of energy, while one gram of starch similarly 



* Arch. path. Anat. u. Physiol, 89, 333. 
t Die Kraftvorrate der Nahrungsstoffe 
% Zeit. f. Biol.. 19, 313. 



THE RELATIONS OF METABOLISM TO FOOD SUPPLY. 153 

oxidized liberates but about 4.2 Cals. The relative values of fat 
and starch, then, are as 9.5:4.2 or as 2.26:1. Similarly, one 
gram of proteids oxidized to carbon dioxide, water, and the nitrog- 
enous metabolic products of feces and urine liberates (in the dog) 
about 4.4 Cals. of energy. So far, therefore, as they are used as 
a source of energy simply and not for constructive purposes, their 
value, compared with starch, would be as 4.4 : 4.2 or as 1.05 : 1. 

A rival theory of "isoglycosic values," the basis of which has 
already been indicated in Chapter II, has been advanced by Chau- 
veau * and his school in Paris. According to this school, dextrose 
(or glycogen) constitutes the material which is consumed in the 
vital activities of the organism. The various nutrients, then, will 
be of value to the organism in proportion to the amount of gly- 
cogen or dextrose which they can supply, and the chemical equa- 
tions already given on pp. 38 and 51 are claimed to show sub- 
stantially what that amount is. The carbohydrates, according to 
this theory, yield practically their entire store of energy to the 
organism, while if the equations mentioned are interpreted liter- 
ally the sugar produced from one gram of proteids would, accord- 
ing to Chauveau's equation, contain but about 1.83 Cals. of poten- 
tial energy in place of the 4.4 Cals. available from the proteids 
according to Rubner. If the proteids are assumed to be split 
up in accordance with Gautier's equation the resulting dextrose 
would contain about 80 per cent, of their potential energy, and 
this figure is used in computing their isoglycosic value. Similarly, 
the sugar derived from one gram of fat would contain about 6.07 
Cals. out of the 9.5 Cals. contained in the original fat. In other 
words, while Chauveau does not question that the actual food of 
the living cells is of value in proportion as it supplies energy, he 
holds that in the complex organism of the higher animals a con- 
siderable share of the original potential energy of fats and proteids 
is lost during their conversion into material (carbohydrates) which 
the cells can use. 

The conception of the mutual replacement of the nutrients on 
the basis of the amounts of energy they are capable of liberating 
for the use of the organism has proved a fruitful one and been the 
basis of much subsequent research. A full discussion of it and 

* La Vie et l'Energie chez FAnimale. 



154 PRINCIPLES OF ANIMAL NUTRITION. 

of the modifications which later investigation has made necessary 
in Rubner's original conclusions, is possible only in connection 
with a general study of the energy relations of the food, the animal, 
and the environment such as forms the subject of Part II. For 
the present we may content ourselves with accepting the general 
idea that the relative values of the nutrients depend in very large 
measure upon their ability to furnish energy for the vital activi- 
ties, deferring until later the consideration of quantitative rela- 
tions. 

The Non-nitrogenous Ingredients of Feeding-stuffs.— 
The discussions of the foregoing paragraphs have had reference to 
the effects produced by pure or approximately pure nutrients upon 
the metabolism of carnivora. By reason of the simplicity of con- 
ditions which is possible in such experiments they are indispensa- 
ble in a study of the fundamental laws of nutrition. We must 
presume also that the general principles established by such 
experiments are applicable to all warm-blooded animals, since 
we know of no radical differences in their vital processes. 

In making such an application to the nutrition of our domestic 
herbivorous animals, however, much caution is necessary to avoid 
unwarranted assumptions and conclusions. Two points need espe- 
cially to be borne in mind : 

First, the food of these animals is, from a chemical point of view, 
very heterogeneous. In addition to true proteids, there are present, 
especially in coarse fodders, various non-proteid nitrogenous sub- 
stances, while the non-nitrogenous nutrients, besides hexose carbo- 
hydrates and true fats, include, on the one hand, pentosans and 
pentoses, lignin, and all the variety of unknown substances com- 
prised under the conventional terms "nitrogen-free extract" and 
" crude fiber, " and on the other the waxes, resins, coloring matters, 
etc., contained in the "crude fat." 

Second, the process of digestion in herbivora, and especially in 
the ruminants, as was pointed out in Chapter I. differs materially 
from that in carnivora as regards the part played by fermentative 
processes, particularly in the solution of the carbohydrates and 
related bodies which are so abundant in vegetable materials- 

It has been more or less customary to regard the digested por- 
tions of the crude fiber and nitrogen-free extract of feeding-stuffs 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 155 

as consisting essentially of carbohydrates. The basis for this 
assumption is the demonstration by Henneberg that the ultimate 
composition of that portion of these two groups of substances 
which is not recovered in the feces is substantially that of starch 
or cellulose, while Kellner * has more recently demonstrated their 
equality in energy value. This fact of itself, however, does not 
justify the inference of equal nutritive value, as may be readily 
seen in the case of starch. It is obviously not a matter of indiffer- 
ence whether a given amount of this substance is resorbed from the 
digestive canal of a steer in the form of sugar or whether, as in some 
of Kuhn's experiments, 65 percent, of it is converted into methane, 
carbon dioxide, and organic acids, yet the elementary composition 
of the " digested " portion would be the same in either case. 

The fact is that while the resorbed food of herbivora contains 
proteids, carbohydrates, and fats, whose functions in nutrition must 
be assumed to be the same as in the carnivora, it is very far from 
consisting entirely of them, but contains also a variety of other 
substances of whose exact nature and proportions we are compara- 
tively ignorant. We know, of course, that the digested non-nitrog- 
enous ingredients of feeding-stuffs, taken as a whole, do serve as 
sources of energy. When an ox or a sheep is fed exclusively on 
ordinary coarse fodders such as hay, straw, or corn stover, the small 
supply of proteids that he receives is likely to be little if any in ex- 
cess of the minimum demand, and the requirements of the body for 
energy must be satisfied very largely by the non-nitrogenous mate- 
rials. Moreover, the supply of such substances as starch, sugars, 
and true fats in such a case is so small relatively that it appears 
difficult to suppose that these alone are sufficient for the needs of 
the organism, and one is forced to the conclusion that the ill-known 
ingredients of the "crude fiber" and " nitrogen-free extract" are 
also utilized. 

The separation and identification of these various substances 
and the study of their physiological effects presents a problem at 
once attractive and laborious and one whose complete solution we 
cannot hope soon to reach. Some few data as to certain classes, 
however, are available. 

* Compare Part II, Chapter X. 



156 PRINCIPLES OF ANIMAL NUTRITION. 

Pentose Carbohydrates. — It has already been shown in Chapter 
II (p. 24) that such of the pentose carbohydrates as have been 
experimented upon are at least partially oxidized in the body, and 
that this appears to be especially the case with herbivora, the urine 
of these animals seldom containing pentoses. 

It is of course conceivable that a substance may be oxidized 
in the body without producing any useful effect except in so 
far as the resulting heat may be of value to the organism, but it 
seems more consonant with our general conceptions of the nature 
of metabolism to suppose that the potential energy of any substance 
which is capable of entering into the metabolism of the cells may be 
utilized as a source of energy for their functions. In the case of the 
pentoses, moreover, we have the additional fact, seemingly well 
established, that pentoses may give rise, directly or indirectly, to a 
production of glycogen. (Compare p. 26.) If we suppose the 
latter body to be formed directly from the pentoses, then their nutri- 
tive value is established, since that of glycogen is unquestionable. 
If, on the other hand, we suppose that the pentoses enable glycogen 
to be produced by protecting other materials from oxidation, then 
their nutritive value is likewise established, since they serve as a 
source of energy to the organism. 

Recent respiration experiments by Cremer * seem to fully con- 
firm this conclusion. In addition to an only partially successful 
trial with a dog, four experiments were made in which the urinary 
nitrogen and the respiratory carbon of rabbits were determined on 
a diet of varying quantities of rhamnose as compared with a preced- 
ing and succeeding day of fasting. No examination of the feces was 
made, except to determine the amount of rhamnose contained in 
them. Small amounts of this substance were also found in the 
urine. Neglecting the carbon and nitrogen of the feces and esti- 
mating the urinary carbon from the nitrogen by the use of Rubner's 
factor, t 0.7462, the following results have been computed, the two 
or three fasting days in each experiment being averaged. The 
amount of rhamnose stated is exclusive of that found in feces and 
urine. 

* Zeit f. Biol., 42, 451. 
-\ Ibid., 19, 318. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 157 



Lost from Body. 




Carbon. 
Grms. 



Experiment I: 
Experiment II: 
Experiment III: 
Experiment IV: 



f Fasting 

\ 11 . 584 grms. rhamnose 

j Fasting 

( 17.09 grms. rhamnose . 

j Fasting 

I 18 . 96 grms. rhamnose . 

j Fasting 

1 24 . 30 grms. rhamnose . 



13.831 
12.020 
16.542 
10.835 
10.742 

5.338 
13 . 383 

4.482 



The conditions in the first experiment were not regarded as 
satisfactory. In the other three the loss of fat from the body was 
notably diminished by the administration of rhamnose, precisely as 
in the experiments of Pettenkofer & Voit and of Rubner (pp. 147 
and 148) with the hexose carbohydrates. The quantitative results 
vary considerably in the individual experiments, but in the second 
and fourth correspond quite closely to the law of isodynamic 
replacement. 

Kellner * computes from the results of respiration experiments 
in which extracted rye straw was added to a basal ration that the 
furfuroids (presumably pentosans) of this material must have con- 
tributed to the production of fat to as great an extent as starch or 
cellulose. (Compare p. 183.) A fortiori, therefore, they must be 
capable of protecting the body fat from oxidation. 

Organic Acids. — Mention was made in Chapter II of the fact 
that the organic acids, which are found to some extent in the food 
and which are produced in large amounts by the fermentation of 
the carbohydrates in the digestive apparatus of herbivora, are oxL 
dized in the body. From this latter fact we should anticipate that 
they might serve as sources of energy to the organism, and this 
anticipation apparently has been confirmed by several investi- 
gators. 

Zuntz & v. Mehring t determined the amount of oxygen con- 
sumed by fasting rabbits before, during, and after the injection 



* Landw. Vers. Stat., 53, 457. 
t Arch, ges Physiol., 32, 173. 



158 



PRINCIPLES OF ANIMAL NUTRITION. 



into the circulation of sodium lactate. The results per kilogram 
and quarter hour were as foUows: 





Before Injection. 




After Injection. 




Quarter hours. 


Injec- 
tion. 


Quarter hours. 




Fourth. 


Third. 


Second. 


First. 


First. 


Second. 


Third. 


Fourth. 




c.c. 


c.c. 


c.c. 


c.c. 


c.c. 


c.c. 


c.c. 


c.c.'' 


c.c. 


Apr. 19... 


184.7 


184.5 


190.1 


183.3 


203.4 


185.4 


199.0 


188.6 


182.2 


" 20... 


155.3 


142.2 


164.1 


155.6 


168.3 


156.6 


158.5 


164.4 


160.0 


" 22a 


142.1 


132.6 


143.5 


138.5 


147.2 


153.6 


153.3 


155.4 


157.4 


" 226 


155.4 


157.4 




157.1 


164.8 


155.3 


160.7 


147.1 


154.1 


" 28... 


159.2 


150.7 


158.5 


155.0 


178.1 


163.2 


158.8 


172.9 


153.9 


May 2 . . . 


176.6 


185.0 


158.2 


173.6 


171.8 


161.8 


173.4 


163.3 


180.2 


4... 


156.1 


167.6 


159.9 


152.4 


166.2 


156.0 


164.2 


159.0 


160.1 


Totals.... 


1129.6 


1120.0 


974.3 


1115.5 


1199.8 


1131.9 


1167.9 


1150.7 


1147.9 


Averages . 


161.4 160.0 162.4 159.4 


171.4 


161.7 166.8 164.4 164.0 




160.8 


164.2 



It being well established that lactic acid is readily oxidized in 
the body (compare p. 27), it is evident that in these experiments it 
must have protected the body fat from being metabolized, since 
otherwise the consumption of oxygen would have increased. Simi- 
lar, although not decisive, results were obtained with sodium buty- 
rate. On the other hand, sodium lactate administered by the 
mouth caused more or less increase in the oxygen cousumption. 
Wolfers * has reported confirmatory results with sodium lactate. 
Munk t injected sodium butyrate into the veins of fasting rabbits 
curarized to eliminate the effects of muscular activity and secure 
uniform metabolism, and determined the respiratory exchange by 
the Zuntz method (p. 72). The oxidation of sodium butyrate 
according to the equation. 

C 4 H 7 Na0 2 + 50 2 = 3C0 2 + 3H 2 + NaHC0 3 

corresponds to a respiratory quotient of 0.6, which is less than that 



* Arch. ges. Physiol., 32, 222. 
f Ibid., 46, 322. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 159 

of the fasting animal. The material lowering of the quotient which 
was observed was therefore interpreted as showing that the sodium 
butyrate was oxidized, and this conclusion was confirmed by the 
strongly alkaline character of the urine and the absence from it 
of butyric acid. The amount of sodium butyrate injected during 
1J to 1^ hours was sufficient in the several experiments to supply 
from 60 to 100 per cent, of the respiratory demand of the fasting 
animal. If this had been oxidized uselessly — that is, if the energy 
liberated had not been of use to the organism — then the consump- 
tion of oxygen and elimination of carbon dioxide should have in- 
creased correspondingly. This, however, was far from being the 
case, as the following fifteen-minute averages for the periods 
before, during, and after the injection show: 



Acid 

Injected, 

Grms. 



Oxygen 
Consumed 



Carbon 
Dioxide 
Excreted, 



Respira- 
tory 
Quotient. 



A nimal I, weight 1 . 92 kgs. : 

Before injection 

During " 

After " 

Animal II, weight 1 . 9 kgs. : 

Before injection 

During " 

After " 

Animal HI, weight 1 .82 kgs. 

Before injection 

During " 

After " 

Animal IV, weight 1 .47 kgs. 

Before injection 

During " 

After " 



0.133 



0.199 



0.206 



0.186 



260.9 
280.0 
253.3 



290.9 
325.2 
299.4 



305.3 
330.9 
306.6 



278.9 
297.6 
278.1 



196.1 
190.5 
181.2 



228.3 
214.6 
230.9 



243.4 
238.0 
235.3 



201.0 
197.9 
205.2 



0.75 
0.68 
0.71 



0.78 
0.66 
0.78 



0.79 
0.72 
0.77 



0.72 
0.68 
0.73 



In place of an increase of 60 to 100 per cent, in the respiratory 
exchange under the influence of the sodium butyrate, there was an 
increase of only 7 to 8 per cent, in the oxygen and none at all in the 
carbon dioxide. It is evident, therefore, that the loss of fat from 
the body must have been largely diminished, the butyric acid serv- 
ing as a source of energy in its place. A stimulating effect upon 



i6o 



PRINCIPLES OF ANIMAL NUTRITION. 



the heart's action was noticed, and Bokai is quoted as having shown 
a similar action on the peristaltic movements of the intestines, and 
these facts perhaps account for some of the increase of the oxygen, 
but Munk shows another reason for most of it. To produce 1 Cal. 
of energy by the oxidation of sodium butyrate he computes to re- 
quire 0.324 gram of oxygen, while to produce 1 Cal. by the oxida- 
tion of fat requires, according to Zuntz & Hagemann (Chapter VTI1), 
0.302 gram or 6.2 per cent, more in the first case. It would thus 
appear that the replacement of fat by sodium butyrate was sub- 
stantially isodynamic. 

Mallevre * experimented with sodium acetate, whose respira- 
tory quotient is 0.5, by the same method as Munk, the amount 
injected equaling 85-100 per cent, of the respiratory demand. The 
results per quarter hour were: 



Weight and Condition. 



Weight, 1.44 kgs.J 
Just after eating.. ) 



Weight, 1.5 kgs.. ( 

After two days' -| 

fasting ( 

Weight, 1.82 kgs. 

After two days' 

fasting 

Weight, 1.7 kgs.. | 

After one day's -J 

fasting 



Sodium 
Acetate 
per Kg. 

Weight, 
Grms. 



Oxygen 

Con- 
sumed, 
c.c. 



I. 

Before injection. 
During " 
Residual effect.. 
After injection. . 

II. 

Before injection. 
During " 
After 

III. 

Before injection 
During " 
After 

IV. 

Before injection 
During " 
Residual effect.. 
After injection. . 



0.201 



0.231 



0.127(?) 



0.152 



176.1 
193.8 
197.7 
178.0 



195.3 
231.8 
211.2 



Carbon 

Dioxide 

Excreted 

c.c. 



1S3.6 
167.1 
152.6 
171.2 



149.6 
168.2 
163.3 



214.7 165.9 

244.8 169.5 



Respi- 
ratory 
iuotient. 



217.1 


166.6 


183.4 


160.5 


208.1 


167.0 


209.5 


164.7 


194.7 


164.7 



1.04 
0.86 
0.76 
0.96 



0.77 
0.71 

0.77 



0.77 
0.69 
0.77 



0.87 
0.80 
0.79 
0.85 



The decrease in the respiratory quotient, as well as the results 
of the examination of the urine, showed that the sodium acetate 



* Arch. ges. Physiol., 49, 460. 



THE RELATIONS OF METABOLISM TO FOOD-SUPFLY. 161 

was oxidized in the body. The increase in the amount of oxygen 
consumed is much more marked than in Munk's experiments, rang- 
ing from 10.4 to 14 per cent. Moreover, as Mallevre points out, in 
the oxidation of sodium acetate about the same volume of oxygen 
is required to produce a unit of heat as in the case of fat. Appar- 
ently, then, while the sodium acetate, like the sodium butyrate in 
Munk's experiments, must have largely diminished the metabolism 
of the body fat, it also stimulated the total metabolism and was 
substituted for the fat in less than the isodynamic ratio. As in 
Munk's experiments, a stimulation of the heart action and also an 
increased peristalsis of the intestines was observed. 

It would seem, then, that lactic and butyric acids, when 
introduced into the circulation of the fasting animal, protect 
the body fat from oxidation, and replace other nutrients in 
isodynamic proportions. Acetic acid, on the contrary, seems in- 
ferior to the other two in this respect, and it is of interest to recall 
that according to Weiske & Flechsig (p. 123) it apparently has 
also less effect in diminishing the proteid metabolism. 

Crude Fiber. — As was stated on p. 117, the early experiments 
by v. Knieriem * upon the nutritive value of cellulose comprised 
respiration experiments as well as determinations of the proteid 
metabolism. Combining the results for nitrogen already given with 
those for carbon, we have the following: 





Number 

of 

Days. 


Food per Day. 
(Two Animals.) 


Gain or 


Loss of 


Period. 


Nitrogen, 
Grms. 


Carbon, 

Grms. 


I 


9 
10 
5 
4 
3 


Milk and horn dust 


-0.599 
+ 0.104 
-0.330 
-0.318 
-0.023 


—4.521 


II 
III 


Same + 18 . 63 grms. crude fiber * . . . 
Milk and horn dust 


-0.434 

—4.868 


IV 

Vf.... 


Same + 11 grms. cane-sugar 

" + 33 " " 


-1.673 
+ 5.653 



* Water-free. 

t Results regarded by the author as of doubtful value. 



In addition to its effect in diminishing the proteid metabolism, 
the crude fiber in these experiments seems to have been fully as 
efficient as the cane-sugar as a substitute for body fat. 
* Zeit. f. Biol., 21, 67. 



I 62 PRINCIPLES OF ANIMAL NUTRITION. 

As we have seen, there has been considerable study of the effects 
of crude fiber on the proteid metabolism, but no other comparative 
experiments appear to have been made regarding the replacement 
values of cellulose and other carbohydrates in a maintenance ration. 

The somewhat lower value which seems to be indicated for the 
organic acids by the experiments cited in the previous paragraph 
has been made the basis of conclusions as to the inferior nutritive 
value of cellulose, and Zuntz,* in some comments on Mallevre's 
experiments, remarks that the apparent equality between cellulose 
and starch observed in experiments on ruminants is to be explained 
by the fact that in these animals the starch also undeigoes 
fermentation, a fact which the researches of G. Kiihn at Mockern 
have since established. In other words, he would say that in case 
of ruminants the starch has as low a value as the cellulose rather 
than that the cellulose has as high a value as the starch. 

Kellner has 'recently obtained results, to be discussed a little 
later, which seem to prove a participation by the digested cellulose 
in actual fat production to as great an extent as by starch, and 
which therefore seem to put the nutritive value of the form of cellu- 
lose used by him beyond dispute. 

Utilization of Excess of Non-nitrogenous Nutrients. — No 
elaborate scientific investigation is needed to teach us that food 
supplied in exceess of the immediate demands of the organism re- 
sults in a greater or less storage of material in the body, this material 
consisting, in the mature animal, largely of fat. But while the fact 
of fat formation is obvious, the exact source of the fat has been the 
subject of as much controversy as almost any physiological question. 
As we have seen in the previous section, opinions are still far from 
being unanimous as to the production of fat from proteids, while 
until quite recently the same might have been said regarding 
the carbohydrates as a source of fat. A very complete critical re- 
view of the literature of the subject of fat formation in the animal 
body was published by Soskin f in 1894, and to this the writer is in- 
debted for a considerable number of the statements and references 
on the succeeding pages. 

As was stated on p. 29, the older physiologists looked upon the 

* Arch. ges. Physiol., 49, 447. 
f Jour, f Landw., 42, 157. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 163 

fat of the food as the sole source of the body fat. The contrary 
view was first propounded by Liebig * in- 1843. After drawing the 
distinction between "plastic materials" (proteids), which serve to 
build up the tissue, and "respiratory materials" (non-nitrogenous 
substances), which serve as sources of heat, he asserts that any 
excess of the latter over the immediate needs of the organism is con- 
verted into fat. This proposition, which was based upon observa- 
tion and general knowledge rather than upon specific experiments, 
led to an active controversy with the adherents of the older view 
and to much direct experimental work. 

Liebig, while not denying that the food fat was a source of body 
fat, maintained that the amount contributed by it was insignificant 
and regarded the carbohydrates as the chief source of animal fat. 
The controversy turned upon the question of the possibility of 
accounting for the body fat by the food fat, both parties tacitly 
agreeing that any excess was to be credited to the carbohydrates. 
The principal champions of the older view were Boussingault, Dumas, 
and Payen.f Boussingault, in particular, brought forward the 
results of experiments on milch cows, according to which the fat 
of the food fully sufficed to account for that in the milk. They 
all, however, ultimately came to acknowledge the substantial accu- 
racy of Liebig's view. Thus Dumas & Milne-Edwards J confirmed 
the results of Huber & Gundlach,§ cited by Liebig, according to 
which bees can produce wax from honey or sugar. Boussingault || 
published the results of new experiments on milch cows as sus- 
taining his previous view of the question, but later ^f convinced 
himself by careful and laborious experiments on the fattening of 
swine and geese of its untenability and of the correctness of Liebig's 
position. Thus in one of his experiments nine pigs gained 103.2 kgs. 
of fat in ninety-eight days, while the food contained but 67.6 kgs., 
of which about 8 kgs. was excreted undigested in the feces. 
Persoz ** likewise, in experiments with geese, obtained similar 

' * Ann. Chem. Pharm., 45, 112; 48, 126; 54, 376. 
"j" Annal. de Chim. et de Physique., 3d ser. 8, 63. 
j Ibid., 14, 400. 

§ Naturgeschichte der Bienen, Kassel, 1842. 
|] Annal. de Chim. et de Physique., 3d ser., 12, 153 
If Loc. ait., 14, 419. 
** Annal. de Chim. et de Physique., 14, 408. 



1 64 PRINCIPLES OF ANIMAL NUTRITION. 

results and also observed a production of fat by these animals when 
fed on food from which all fat had been removed. 

Fat. — That the fat of the food may serve directly as a source of 
body fat has been shown by Hofmann,* who fasted a dog for thirty 
days, thus rendering the body almost fat-free, and then fed for five 
days large amounts of fat bacon containing as little lean meat as 
possible, and from which there were digested daily 370.8 grams of 
fat and 49.4 grams of protein. At the end of the five days the 
body of the animal contained 1352.7 grams of fat. Estimating its 
fat content at the close of the fasting period at 150 grams, there was 
produced daily about 240 grams of body fat. According to the 
highest recorded estimates not over 26 grams of this could possibly 
have been formed from the protein of the food. Hofmann also 
shows from the result of one of Pettenkofer & Voit's respiration 
experiments, in which meat and fat were fed, that part of the ob- 
served gain of fat must have had its source in the fat of the 
food. 

The latter investigators also showed in the last of the experi- 
ments cited on p. 144 that a large ration of fat alone may result in a 
considerable storage of fat. Most of the experiments by the same 
investigators in which lean meat and fat were fed show not merely a 
diminution of the loss of body fat but an actual increase in its 
amount. (Compare the averages on page 150.) The fact is most 
strikingly shown, however, in a series in which increasing amounts 
of fat were added to a uniform ration of meat which was itself 
sufficient to maintain both nitrogen and carbon equilibrium. The 
results as given by Pettenkofer & Voit f are contained in the table 
at the top of p. 165, those on the basal ration of meat being the 
same as those given also on p. 109 for the first series. 

It is of course possible to interpret these results as showing that 
the fat of the food was oxidized and protected an equivalent amount 
of the non-nitrogenous residue of the proteids from oxidation and 
that the latter were the real source of the fat gained. No necessity 
for such an interpretation is apparent, however, and the direct 
explanation appears the simpler and more natural. 

The results of experiments upon the deposition of foreign fats 

* Zeit. f. Biol., 8, 153. 
t Ibid., 9, 30. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 165 



Number 

of 
Trials. 


Food. 


Nitrogen 

of 
Excreta. 


Total Carbon 

of 

Excreta. 


Gain or Loss of 


Meat. 


Fat. 


Flesh. 
(N-f-0.034.) 


Fat. 


3 
2 
1 

2 
1 
2 


1500 
1500 
1500 
1500 
1500 
1500 




30 

60 

100 

100 

150 


51.0 
49.6 
51.0 
47.7 
49.3 
49.5 


184.5 
180.6 
203.6 
182.4 
174.4 
193.1 




+ 42.8 
- 0.6 
+ 97.8 
+ 49.4 
+ 44.8 


+ 4.3 
+ 32.4 
+ 39.4 
+ 91.1 
+ 109.5 
+ 135.7 



in the body which were considered in Chapter II, p. 30, also testify 
to the direct formation of body fat from food fat. 

Carbohydrates. — Among the experiments of Pettenkofer & 
Voit which have been cited in the foregoing pages are several which 
show a production of fat upon a ration of lean meat with the addi- 
tion of starch or dextrose or of starch alone. A more complete 
summary of these experiments * is given below: 





i umber 

of 
Rxperi- 
ments. 


Food per Day. 


Gain or Loss of 




Meat 

Grm.5. 


Fat. 
Grms. 


Carbo- 
hydrates. 
Grms. 


Proteids, 
Grms. 


Fat, 
Grms. 


Proteids and dextrose 

r 

Proteids and starch 1 


1 
1 

3 
3 
1 
8 
1 
2 
1 


'566 

400 

500 

800 

1500 

1800 


16.9 
21.2 
20.2 

5.6 

5.3 

13.7 

4.5 
10.1 


450 
597 
700 
200 
400 
200 
450 
200 
450 


-45.0 
-58.8 
-38.8 

- 8.1 

- 3.1 
-11.3 
+ 40.6 
+ 6.3 
+ 70.6 


+ 56.2 
+ 3.4 
+ 106.4 
+ 15.0 
+ 109.9 
+ 19.5 
+ 71.5 
+ 18.1 
+ 126.5 



Pettenkofer & Voit's Conclusions. — In discussing these results 
Pettenkofer & Voit assumed that, as computed by Henneberg,t 100 
grams of proteids can give rise to a maximum of 51.4 parts of 
fat. On this basis they found that, with two apparent exceptions, 
the fat of the food, together with that which could be derived from 

* Zeit f. Biol., 9, 435. 

f Landw. Vers. Stat., 10, 455, foot-note. 



1 66 PRINCIPLES OF ANIMAL NUTRITION. 

the amount of proteids metabolized, was sufficient to account for 
the gain of fat. They therefore concluded that the carbohydrates 
simply protected these materials from oxidation and regarded the 
formation of fat from the former as improbable, being confirmed 
in this belief by the observation that the amount of fat produced 
was proportional to the proteids rather than to the carbohydrates 
of the food. The apparent exceptions they regarded as due to a 
retention of undigested starch in the alimentary canal. In brief, 
Pettenkofer & Voit, while not denying that carbohydrates aid in 
the production of fat, regarded their action as an indirect one. 

It should be added that, contrary to the general impression, Voit 
did not absolutely deny the formation of fat from carbohydrates, 
but regarded it as improbable and unproved. Moreover, he came 
later to admit the truth of the opposite view, and even furnished 
from his laboratory experimental evidence in its support. 

At an earlier date Voit * had likewise made experiments on a 
milch cow, the result of which was that not only all the fat of the 
milk, but most of the milk-sugar as well, could be accounted for by 
the proteids and fat of the food. Voit also examined the numerous 
experiments of Dumas, Persoz, Boussingault, and others (p. 163) 
upon the origin of animal fat and satisfied himself that, although 
they undoubtedly showed, as their authors claimed, a formation 
of fat from other ingredients of the food, the amount produced 
could at least in the great majority of cases be accounted for by 
the proteids of the latter. 

It is important to observe that the evidence supporting Voit's 
view was negative evidence. The results could be explained on the 
hypothesis that the carbohydrates did not contribute to fat pro- 
duction, but while a large number of such results might render the 
hypothesis very probable, they could not demonstrate its truth. On 
the other hand, even a single well-authenticated case in which the 
fat and proteids of the food did not suffice to account for the amount 
of fat formed in the body would suffice to establish the possibility 
of its formation from other materials. A few apparent cases of this 
sort among earlier experiments Voit was able to explain plausibly, 
but there was one important exception, viz., the experiments of 

* Zeit. f. Biol., 5, 79-169. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 167 

Lawes & Gilbert * at Rothamsted, in 1850, on the fattening of 
swine. 

Lawes & Gilbert's Investigations. — These experiments consti- 
tuted part of a series of feeding trials with fattening sheep and pigs, 
undertaken to test the then current view of Boussingault, according 
to which the feeding value of stock foods was proportional to their 
content of nitrogen. From the results of their extensive experi- 
ments, Lawes & Gilbert concluded that in fattening animals both 
the amount of food consumed by a given weight of animal within a 
given time and the increase in weight obtained are measured rather 
by the supply of non-nitrogenous than of nitrogenous constituents 
in the food. This fact of itself strongly suggests a production of 
fat from carbohydrates. 

In connection with these feeding trials investigations were also 
made into the composition of the increase in live weight during 
fattening.f By a comparison of the weight and composition of 
one of the fattened pigs with those of an animal supposed to be 
precisely similar at the beginning of the fattening the percentage 
composition of the increase was found to be approximately: 

Water 28.61 

Ash 0.53 

Proteids 7 . 76 

Fat 63.10 

100.00 

During the ten weeks of the fattening the animal gained 88 
pounds, containing according to the above figures 55.5 pounds of 
fat, while the total food consumed contained but 13.7 pounds. In 
other words, over three fourths of the fat was formed from other 
ingredients of the food. 

After the publication of Voit's first paper, Lawes & Gilbert t 
presented the results of this and eight other experiments in their 

* Report British Association Adv. Sci., 1852; Jour. Roy. Agr. Soc, 14, 
459; Rep. British Asso. Adv. Sci., 1854; Rothamsted Memoirs, Vol. II. 

t Jour. Roy. Agr. Society, 21, 465; Phil. Trans., Part II, 1859, p. 493. 

t Rep. British Asso. Adv. Sci., 1866; Phil. Mag., Dec, 1866; Rotham- 
sted Memoirs, Vol. IV. 



i68 



PRINCIPLES OF ANIMAL NUTRITION. 



bearing on the origin of the fat. Nos. 2 to 5 were selections from 
the first two series of the experiments of 1850 (designated as I and 
II in the table below) and Nos. 6 to 9 were experiments upon the 
equivalency of starch and sugar in food reported in 1854 * (desig- 
nated below by S) . The following table shows the original numbers 
of the several experiments and the character of the food consumed : 



No 


Original Designation. 


Food. 




Series. 


Number. 




1 
2 
3 
4 
5 
6 
7 
8 
9 


i 

i 

i 

ii 

s 
s 
s 
s 


12 
1 
5 
5 
1 
2 
3 
4 


Bean meal, lentil meal, bran, and barley meal ad lib. 

Bean meal, lentil meal, bran, and corn meal ad lib. 

Bean meal and lentil meal ad lib. 

Corn meal ad lib. 

Barley meal ad lib. 

Lentil meal and bran, with sugar ad lib. 

Lentil meal and bran, with starch ad lib. 

Lentil meal and bran, with sugar and starch. 

Lentil meal, bran, sugar, and starch ad lib. 



From the results of the first experiment, the amount of fat con- 
tained in the observed increase in live weight in each case was com- 
puted, the animals being assumed to have had at the beginning of 
the fattening the composition of the lean pig analyzed and at its 
close that of the fat pig. These amounts were then compared with 
the amounts which could have been produced from the fat and pro- 
teids of the food. In order to make the case as unfavorable as 
possible for the carbohydrates the authors assumed: 

First, that all the fat of the food was digested and laid up in the 
body. 

Second, that all the nitrogenous matter of the food was digested, 
and that it all consisted of true proteids. 

Third, that, after deducting the amount of proteids gained by 
the body, the total carbon of the remainder, minus that required to 
form urea, was available for fat formation. 

The results of the comparison were as follows, calculated per 
100 pounds gain in live weight- 



*Rep. Brit. Asso. Adv. Sci., 1854. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 





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170 PRINCIPLES OF ANIMAL NUTRITION. 

Even on the most extreme assumptions it is only possible to 
regard the fat produced as derived wholly from the proteids of the 
food in three cases in which an excessive proportion of the latter was 
fed. If the probable digestibility of the foods used be considered, 
and Henneberg's factor (51-4 per cent.) for the possible production 
of fat from proteids be used, the results show even more decidedly 
a formation of fat from carbohydrates. In a later paper,* in reply 
to criticisms, the authors state that they have reviewed and recal- 
culated many of their experiments with the result that, while the 
experiments with ruminants (sheep and oxen) failed to furnish con- 
clusive evidence of the formation of fat from carbohydrates, a 
large number of those with pigs unquestionably showed such for- 
mation. 

In view of their historical interest it has seemed desirable to 
give the results of Lawes & Gilbert's experiments in some detail, 
although at the time they hardly secured the recognition which 
was due them and Voit's views became the generally accepted 
theory for the next twenty-five years. Notwithstanding the latter 
fact, however, results of experiments on herbivorous animals speed- 
ily began to accumulate which were difficult to reconcile with Voit's 
hypothesis. 

Experiments on R uminants. — Experiments on milch cows were 
made by Voit himself, as already noted. G. Kuhn & Fleischer f 
a little later discussed the results of two of their extensive feeding 
experiments on milch cows in their bearing on this point, and M. 
Fleischer J did the same with the results of similar experiments 
made by Wolff and himself. § Their results are tabulated on the 
opposite page. 

Neither Voit's nor Fleischer's results are such as to require the 
assumption of a formation of fat from carbohydrates. Those of 
Kuhn & Fleischer show a small excess of fat in the milk over that 
producible from the fat and proteids of the food, but the authors 



* Jour. Anat. and Physiol., 9, 577; Rothamsted Memoirs, Vol. IV. 

t Landw. Vers. Stat., 10, 418; 12, 451. 

% Virchow's Archiv, 51, 30. 

§ Jour. f. Landw., 19, 371, and 20, 395. 



THE RELATIONS OF METABOLISM TO FOOD SUPPLY. 171 



Y •, . j Experiment a 

Kuhn & Fleischer: | Experiment 1L 
Fleischer: | Experiment L. . 



Fat of 

Fodder, 

Grms. 


Fat from 
Protein, 
Grms. 


Total, 
Grms. 


318.8 


401.8 


720.6 


276.0 


308.5 


584.5 


183.5 


79.5 


263.0 


183.5 


69.5 


253.0 


170.5 


158.5 


329.0 


166.5 


170.0 


336.5 



Fat of 

the Milk, 

Grms. 



577.5 
337.3 
277.5 
292.0 
303.5 
290.5 



regard the differences as within the limits of error in such experi- 
ments. 

Studies of the results of fattening experiments with ruminants 
give similar results. On the basis of Lawes & Gilbert's determi- 
nations of the composition of the increase of live weight in fattening, 
the amount of fat produced in such an experiment may be approxi- 
mately computed and compared with the amounts of proteids and 
fat in the food. Such a comparison by the writer * in seventy-seven 
experiments on sheep showed that, with one or two possible excep- 
tions, the fat and proteids of the food were sufficient to account for 
the amount of fat formed, although in some of the experiments 
little margin was left. 

Experiments on Swine. — Experiments with swine, on the other 
hand, as Wolff f has shown, have almost without exception given 
results which can scarcely be explained except upon the hypothesis 
of a formation of fat from carbohydrates. These animals, as Lawes 
& Gilbert pointed out in their early papers, are especially adapted 
to experiments of this sort, since they consume a relatively large 
amount of easily digestible food, have a small proportion of offal to 
carcass, and are by nature inclined to lay on fat readily. It was 
therefore to be expected that experiments upon swine would show 
a production of fat from carbohydrates, if such took place, more 
decisively than those upon ruminants. 

Experiments on pigs by Weiske & Wildt,J it is true, on the 
same plan as those by Lawes & Gilbert, yielded results consistent 
with Voit's theory, showing a formation of 5565 grams of fat in the 



* Manual of Cattle Feeding, p. 177. 

f Ernahrung Landw. Nutzth., pp. 354-356 

t Zeitschrift f. Biol., 10, 1. 



I7 2 PRINCIPLES OF ANIMAL NUTRITION. 

body as compared with a possible 6724 grams from the fat and 
proteids of the food. The feeds used, however, were not well suited 
to young animals and the gain was abnormally small in proportion 
to the food consumed, so that the results could not be expected to 
be decisive. Moreover, the presence of non-proteid nitrogen in the 
food is not considered in the computation. (See the next paragraph.) 

Sources of Uncertainty. — Up to this point the results of experi- 
ments on herbivorous and omnivorous animals had been somewhat 
conflicting. Before taking up the later investigations it is desir- 
able to point out some of the uncertainties attaching to experiments 
such as those above enumerated. These relate, first, to the amount 
of fat actually produced, and second, to the possible sources of 
supply in the food. 

The basis for estimating the amount of fat actually produced by 
a fattening animal was in two cases a comparison with the amount in 
a supposedly similar animal at the beginning of the fattening, the 
fattened animal being actually analyzed. In the remainder the 
increase in live weight was assumed to have the composition found 
by Lawes & Gilbert. It need scarcely be pointed out that the 
results of such comparisons can be only approximate and are sub- 
ject to a considerable range of error. Only the most decided 
results one way or the other can be accepted as at all conclusive. 
In experiments on milch cows the production of milk fat can of 
course be determined, but the variations in the weight of such an 
animal often render any conclusions as to gain or loss of body fat 
so difficult that the results as a whole are less satisfactory than 
those on fattening. 

The possible sources of fat in the food, aside from the carbohy- 
drates, are the ether extract and the proteids. As regards the first, 
it is certain that not all the digestible ether extract of stock foods 
is true fat. With the proteids the case is still worse. In particu- 
lar we now know that a portion, and in some cases a considerable 
portion, of the total nitrogenous matter of feeding-stuffs consists of 
non-proteid material, which so far as we know contributes little if 
anything directly to fat production. This is a very important source 
of error. Thus the writer * has shown, as has also Soxhlet,f that if 

* Manual of Cattle Feeding, p. 1S2. 

t Compare Soskin, Jour. f. Landw., 42, 203. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 173 

account be taken of this fact the teachings of Weiske & Wildt's 
experiment cited above are exactly reversed and show a formation 
of fat from carbohydrates. A consideration of the same fact, of 
course, tends to make the results of all similar experiments, includ- 
ing those on milch cows, more favorable to the carbohydrates. 

Still further, it is doubtful whether 100 parts of proteids can 
actually yield 51.4 parts of fat. The latter number was computed 
by Henneberg from the elementary composition of proteids and of 
urea to be the maximum amount obtainable. Zuntz,* however, 
has called attention to the fact that if the proteids actually split up 
in the manner which Henneberg's calculation supposes, the products 
must contain all the potential energy of the original material, so 
that none can be given off during their cleavage. This is a process 
wholly without analogy in the animal body, and, to say the least, 
very improbable. It would seem then, that even if we still hold to 
a formation of fat from proteids, we must considerably reduce our 
estimate of its amount. 

Later Fattening Experiments. — All these considerations tend to 
strengthen the belief that fat is formed from carbohydrates, and 
more recent experiments have demonstrated that such is the fact. 
Henneberg, Kern, & Wattenberg.f in experiments undertaken to 
determine the rate of gain and the composition of the increase of 
fattening sheep, and conducted substantially like those of Lawes 
& Gilbert on swine, were the first to furnish proof of the formation 
of fat from carbohydrates by ruminants. Wolff \ having pointed 
out that their results demonstrated that fact, Henneberg discussed 
this feature of the experiments in a later publication. § Regarding all 
the digested ether extract of the food as pure fat, and assuming that 
all the digested nitrogenous matters were true proteids capable of 
yielding 51 .4 per cent, of fat, he obtained the results given on p. 174. 
Forty-two per cent, more fat was produced than could be accounted 
for by the fat and proteids of the food, even on the extreme 
assumptions made. Furthermore, not only did some of the 
nitrogenous substances of the food undoubtedly consist of non-pro- 

* Landw. Jahrb., 8, 96. 

f Jour. f. Landw., 26, 549. 

% Landw. Jahrb., 8, 1. Supp., 269. 

§ Zeit f Biol , 17. 345. 



174 



PRINCIPLES OF ANIMAL NUTRITION. 



Digested 

Proteids stored up 

Proteids available for fat production. 
Equivalent fat (51 .4 per cent.) 

Total from fat and proteids 

Actually produced by animal 



Proteids, 
Grms. 


Fat, 
Grms. 


10220 
936 


2100 


9284 


4772 

6872 
9730 



teids, but a high figure was assumed for their digestibility, and in 
computing the gain of fat by the animal no account was taken of 
the fat of the wool and of the offal. Henneberg's final conclusion 
is that no possible errors arising from differences in the animals 
compared or from irregularities in the consumption of food can 
explain away the above result. 

Soxhlet * made similar experiments with swine fattened on rice, 
that is, on a feeding-stuff poor in proteids and fat and rich in carbo- 
hydrates, with the result that only 17 to 18 per cent, of the fat pro- 
duced could be accounted for by the digestible protein and fat of 
the food. In two experiments with the same species of animal by 
Tschirwinsky f but 43 per cent, and 28 per cent, respectively of the 
fat production could be thus accounted for. Of six experiments 
on geese by B. Schulze, \ four, in which a comparatively wide nutri- 
tive ratio was used, showed that at least from 5 to 20 per cent, of the 
fat must have been produced from carbohydrates. Chaniewski § 
likewise experimented on geese and obtatined much more decisive 
results, from 72 to 87 per cent, of the observed fat production being 
necessarily ascribed to the carbohydrates. 

Recent experiments by Jordan || have shown that the dairy cow 
may likewise produce fat from carbohydrates. In the first experi- 
ment a cow weighing 867 pounds was fed for fifty-nine days with 
food from which most of the fat had been extracted, the digestible 



* Bied. Centr. Bl. Ag. Chem., 10, 674. 

t Landw. Vers. Stat., 29, 317. 

% Landw. Jahrb., 11, 57. 

§ Zeit. f. Biol., 20, 179. 

|| N. Y. State Experiment Station, Bulls. 132 and 197. 



THE RELATIONS OF METABOLISM TO FOOD SUPPLY. 1 75 

protein of the ration being varied from 184 grams to 841 grams per 
day. During this time she gained 33 pounds in weight, and her 
whole appearance was such as to negative the assumption of any 
considerable loss of body fat. In the second experiment one cow 
was fed a ration poor in fat, one a normal ration, and one a ration 
unusually rich in fat, the protein supply being again varied through 
a considerable range. As in the previous case the gain in weight 
and the general condition of the cows forbade the assumption that 
body fat was drawn upon to any material extent. In all instances 
except the last a considerable formation of fat from carbohydrates 
was shown. 

The following table gives the more important data of the above 
experiments : 



Experimenter. 



Henneberg, Kern, 
Wattenberg 

Soxhlet 

Tschirwinsky 

Schulze 

Chaniewski 

59 days 
Jordan: -^74 " 
4 " 



Animal. 



Sheep 
Swine \ 

Swine -j 
f 

Geese ■{ 

Geese 
Cows 



Total 
Proteid* 

Meta- 
bolism, 

Grms. 



9,284 

3,463 

7,169 

5,934 

2,361j 

1,054 

1,049 

785 

785 

555 

555 

110 

203 

100 

15,109 

34,661 

2,209 



Equiva- 
lent Fat, 
Grms. 



4,772 
1,779 
3,685 
3,050 
1,213 
383| 
381 $ 
286$ 
286$ 
194 J 
194$ 
55 
105 
51 
7,766 
17,816 
1,131 





Total 


Fat of 




Food, 




Grms. 


Proteids, 




Grms. 


2,100 


6,872 


300 


2,079 


340 


4,025 


656 


3,706 


203 


1,416 


222 


605 


221 


602 


205 


491 


205 


491 


203 


397 


203 


397 


20 


75 


32 


137 


9 


60 


1,490 


9,256 


2,211 


20,027 


1,504 


2,635 



Fat 

Actually 

produced, 

Grms. 



9,730 

10,082 

22,180 

8,577 

5,429 

387 

539 

515 

612 

492 

471 

269 

640 

445 

17,585 

37,637 

3,289 



In view of the extreme assumptions made in these computations 
as to the possible contribution by the proteids and fat of the food 



* Digested protein of food less gain of protein by the animal, 
f In original 2572 grms. 

% Computed on a different basis from the other experiments 
foe. cit , p. 84. 



Compare 



iy6 



PRINCIPLES OF ANIMAL NUTRITION. 



to fat production, and of the very large differences between this 
amount and the fat computed to have been actually formed, the 
possible errors of the method are relatively insignificant, and these 
investigations, together with the earlier ones, must be regarded as 
establishing the fact of a formation of fat from carbohydrates. 

The earliest experiment to be published in full demonstrating 
the production of fat from carbohydrates in the body of the dog, 
was by Munk.* The animal was deprived of food long enough to 
render it certain that but traces of fat remained in the body. It 
was then fed for twenty-four days on a diet consisting of small 
amounts of meat, with some gelatine, and large quantities of 
starch and sugar. In the body of the animal at the close of the 
experiment 1070 grams of fat were found, of which Munk estimates 
that at least 960 grams must have been produced during the experi- 
ment, while the proteids fed could have produced as a maximum 
only 415.3 grams and the meat itself contained but 75 grams of fat. 
Even if a formation of fat from gelatine be admitted, a considerable 
excess of fat remains unaccounted for except by the carbohydrates 
of the food. 

Respiration Experiments. — There are not wanting, however, for 
final demonstration, experiments with the respiration apparatus, in 
which the total income and outgo of nitrogen and carbon has been 
determined. 

Meissl, Strohmer, & Lorenz,t in very carefully conducted respi- 
ration experiments upon swine, using a wide, a medium, and a 
narrow nutritive ratio, obtained the following results: 



Food, 

Grras. 



Rice 

Barley 

Flesh meal, rice, and 
whey 



Proteid 

Metabolism 

Grms. 



65.4 
64.1 
88.0 

381.6 



Equivalent 
Fat, 
Grms. 



33.6 
33.0 
45.2 

196.1 



Fat of 
Food, 
Grms. 



7.9 
16.4 
15.2 

48.6 



Total 

from Fat 

and Proteids, 

Grms. 



41.5 
49.4 
60.4 

244.7 



Fat 

Actually 

Produced, 

Grms. 



353.9 
413.2 

208.7 

256.3 



Almost simultaneously C. Voit J gave a preliminary account of 

* Virchow's Archiv, 101, 91. 

t Zeit. f. Biol., 22, 63. 

$ Sitzungsber bayr. Acad d. Wiss.; Math. Phys. Classe, 1885, p. 288. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 177 

respiration experiments made in his laboratory by Lehmann & 
E. Voit with geese and by Rubner with a dog which demonstrated 
a production of fat from carbohydrates. Rubner's experiment was 
shortly afterward published in full.* It was a respiration experi- 
ment covering four days immediately following a fortnight's heavy 
feeding with meat. On the first two days of the experiment the 
animal fasted and on the second two received only starch and cane- 
sugar. The results for the last two days were: 

Proteid metabolism 15.94 grams. 

Equivalent fat, according to Rubner.. 7.65 " 

Fat of food 9.40 " 

Maximum from fat and proteids 17 . 05 " 

Fat actually produced 1 17 . 25 " 

Even after making all possible deductions for the fact that some 
carbon may have been retained in the body in the form of glyrogen 
instead of fat, and also for a possible residue of undigested starch in 
the alimentary canal at the close of the experiments, Rubner still 
computes that at least 40.7 grams of fat must have had its origin 
in carbohydrates. 

Lehmann & E. Voit's experiments have only recently ap- 
peared.! In their introduction they report also the results of ex- 
periments on fattening geese made by C. Voit several years previous 
to 1883, which likewise show a production of fat from carbohydrates. 

G. Kiihn and his associates, J at the Mockern Experiment Station, 
have demonstrated, by means of respiration experiments in which 
starch was added to rations but slightly exceeding the maintenance 
requirement, a formation of fat from carbohydrates by ruminants 
(oxen). In view of the possibility (see p. 27) that part of the car- 
bon of the urine may be derived from the non-nitrogenous matter 
of the food, and in order to be on the safe side, the authors assume 
as possible that all the carbon of the proteids metabolized may 
have been stored up in the body in the form of fat. On this extreme 
and improbable assumption their results were as shown on the 
following page : 

* Zeit. f. Biol., 22, 272. 

t Ibid., 42, 619. 

% Reported by Kellner; Landw. Vers. Stat., 44, 257. 



1 7 8 



PRINCIPLES OF ANIMAL NUTRITION. 



Animal. 


Period. 


Proteid 

Metabolism, 

Grms. 


Equivalent 

Fat, 

Grms. 


Fat of 
Food, 
Grms. 


Maximum 

from Fat 

and Proteids, 

Grms. 


Fat 
Actually- 
Produced, 
Grms. 


I 


2a 


373.6 


259 


86 


345 


423 


I 


2b 


382.0 


265 


81 


346 


332 


II 


2 


297.4 


206 


77 


283 


434 


III 


2 


104.4 


' 72 


60 


132 


281 


IV 


2 


126.9 


88 


60 


148 


160 


III 


3 


506.9 


351 


69 


420 


375 


IV 


3 


548.8 


380 


74 


454 


388 


III 


4 


980 


679 


84 


763 


526 


V 


2a 


232 


161 


42 


203 


396 


V 


2b 


268 


186 


42 


228 


407 


V 


3 


149 


103 


39 


142 


703 


VI 


2a 


218 


151 


40 


191 


304 


VI 


26 


232 


161 


35 


196 


381 


VI 


3 


186 


129 


43 


172 


507 



In most of these experiments the rations were purposely made 
poor in proteids and fat, and in all such cases, with one exception, a 
formation of fat from carbohydrates is clearly demonstrated. In 
three cases in which large amounts of proteids were fed, as well as in 
some similar experiments not included in the above table, it was 
possible to account for the fat production otherwise, but such nega- 
tive results in no degree weaken the positive teaching of the remain- 
ing trials. 

The more recent investigations of Kellner et al* at the same 
Station, in which starch was added to a basal ration, although under- 
taken primarily for other purposes, likewise show the formation of 
an amount of fat inconsistent with the hypothesis of its production 
from the fat and proteids of the ration only. 

The failure of Pettenkofer & Voit to obtain affirmative results 
in their earlier experiments appears to be largely explicable, in the 
light of more recent knowledge, from the conditions of the experi- 
ments themselves. Pfliiger f has recalculated their experiments on 
the same basis as those upon the formation of fat from proteids 
(see p. 109), and has pointed out that in the majority of cases the 
total food was, according to his computations, scarcely more than 
sufficient for the maintenance of the organism, thus. leaving no 
excess of any kind for fat production. Moreover, out of those ex- 

* Landw. Vers. Stat , 53, 1. 
t Arch. ges. Physiol , 52, 239. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 179 

periments in which the conditions were favorable for a production 
of fat from carbohydrates, some actually do show that result, al- 
though they were classed by Voit as " exceptional cases," while its 
failure to appear in others is explained, according to Pfliiger, by the 
increased metabolism due to maltreatment of the animal and the 
overloading of its digestive organs with starch. 

Whether we admit all of Pfliiger' s criticism or not, it is now uni- 
versally conceded that the carbohydrates are an important source 
of fat. If we are to go further and deny with Pfliiger the production 
of fat from proteids, we. are brought back, by a curious reversal of 
views, substantially to Liebig's classification of the nutrients into 
" plastic " and " respiratory, " but, as already pointed out, it ap- 
pears altogether probable that the proteids also contribute to fat 
production. However this may be, it is clear that in the case 
of herbivorous animals, which ordinarily consume relatively little 
proteids and fat and large amounts of carbohydrates, the latter are 
the most important factors in fattening, and the results of Lawes 
& Gilbert (p. 167), according to which the gain of fattening ani- 
mals is largely determined by the supply of non-nitrogenous matters 
in the food, are seen to be in full accord with the most careful physi- 
ological investigation. 

Evidence from Respiratory Quotient. — The formation of fat from 
carbohydrates is a process of reduction. If we suppose all the car- 
bon of 100 parts of dextrose, together with the necessary hydrogen 
and oxygen, to be united to form fat of the average composition 
stated on p. 61, we have the following: 





Dextrose. 


Equivalent, 
Fat. 


Residue. 


Equivalent, 
Water. 


Excess of 
Oxygen. 




40.00 

6.67 

53.33 


40.00 
6.28 
6.01 








Hydrogen 


0.39 
47.32 


0.39 
3.12 




Oxygen 


44 20 








100.00 


52.29 


47.71 


3.51 


44.20 



The excess of oxygen we may further suppose to unite with the 
carbon of 41.44 additional parts of dextrose, producing 60.78 parts 
of carbon dioxide and 24.86 parts of water. The process would be 
an intra-molecular combustion analogous to a fermentation, pro- 



I So PRINCIPLES OF ANIMAL NUTRITION. 

during carbon dioxide without the intervention of oxygen from out 
side. The latter fact, of course, is equally true whatever substance 
combines with the excess of oxygen of the carbohydrate. The 
tendency, therefore, will be to increase the respiratory quotient and, 
if large amounts of carbohydrates are thus transformed, to even 
raise it above unity. 

Numerous such instances are on record. Thus Regnault & 
Reiset * report a quotient of 1.024 in case of a hen, and Reiset f ob- 
tained quotients of 1.004 and 1.054 with a ewe and a boar. Han- 
riot & Richet,J in studies on the respiration of man, found that 
the ingestion of carbohydrates caused the respiratory quotient to 
rise markedly and sometimes to exceed unity. Later Hanriot § 
studied the transformations of glucose in the organism of man and 
obtained similar but more marked results, the quotient reaching as 
high a value as 1.28. 

Magnus-Levy || has likewise observed quotients greater than 
unity in the case of a dog fed large quantities of carbohydrates, and 
Bleibtreu,^[ in experiments on fattening geese in a form of Regnault 
respiration apparatus, also verified this fact, as have Kaufmann ** 
and Laulanie ft m experiments upon dogs with sugar. The exten- 
sive respiration experiments of Zuntz & Hagemann \\ on the horse 
also afford numerous instances of respiratory quotients greater 
than unity. 

The evidence of the respiratory quotient, then, is entirely in 
accord with the conclusions reached by other methods as to the 
formation of fat from carbohydrates. 

Non-nitrogenous Nutrients of Feeding-stuffs. — It has 
become customary to regard the digestible non-nitrogenous ingre- 
dients of feeding-stuffs, aside from the ether extract, as consisting 
essentially of carbohydrates. As has several times been urged on 

* Ann de Chim. et de Phys. [3], 26, 45. 

t Ibid. [3], 69, 145. 

t Comptes rend., 106, 419 and 496. 

§ Archives de Physiol., 1893, p. 248. 

|] Arch. ges. Physiol., 55, 1. 

^ Ibid., 56,464; 85, 366. 
** Archives de Physiol., 1896, 341. 
ft Ibid., 1896, 791. 
XX Landw. Jahrb., 27, Supp III. 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 181 

preceding pages, however, this is far from being the case as regards 
the materials actually resorbed from the digestive tract of our 
common domestic animals, particularly the ruminants. A demon- 
stration of the production of fat from carbohydrates, therefore, 
does not necessarily show that the chemically diverse materials 
resorbed from coarse fodders, e.g., are available for fat produc- 
tion. 

As a matter of fact, however, what a large proportion of the 
experiments just cited actually show, under a strict interpretation, 
is that fat was produced from the non-nitrogenous nutrients of the 
rations other than fat. In many of the experiments, it is true, nota- 
bly those with swine and with geese, the ration consisted of concen- 
trated feeding-stuffs whose " nitrogen-free extract " consisted to a 
large extent of hexose carbohydrates. Similarly, in G. Kiihn's ex- 
periments the fat production was secured by the addition of starch 
to rations slightly above the maintenance requirement. In these 
cases, therefore, at least the larger part of the fat production in 
excess of that possible from proteids and food fat must be ascribed 
to the hexose carbohydrates. In experiments like those of Henne- 
berg, Kern & Wattenberg, and of Jordan, on the other hand, a 
not inconsiderable proportion of the non-nitrogenous nutrients 
was necessarily derived from coarse fodders and was, therefore, 
largely of undetermined nature. In such cases it is obviously im- 
possible to say whether the fat production was at the expense of 
the hexose carbohydrates only or whether the other non-nitrog- 
enous ingredients participated in it. 

Other considerations, however, seem to render a participation 
of these substances in fat production, directly or indirectly, at least 
highly probable if not certain. 

Crude Fiber. — The experiments of v. Knieriem (p. 161), as we 
have seen, seem to show that digested cellulose may be as efficient as 
other carbohydrates in protecting the body fat, — that is, as part 
of a maintenance ration. The numerous experiments cited on 
pp. 117-123 likewise indicate that it has an effect similar to that of 
other carbohydrates in diminishing the proteid metabolism. Kell- 
ner * has also investigated its value in a fattening ration, using for 
this purpose the material resulting from the treatment of rye straw 
* Landw. Vers. Stat., 53, 278. 



182 



PRINCIPLES OF ANIMAL NUTRITION. 



with an alkaline solution under pressure and containing 76.78 per 
cent, of "crude fiber." This material was added to a basal ration 
somewhat more than sufficient for maintenance. The results as 
regards the proteid metabolism have already been considered 
(p. 121); the following table shows the effects also upon the fat 
production : 







Apparently Digested. 


Gain. 




Crude j Crude 
Fat, 1 Fiber, 
Grms. j Grms. 


N.-free 
Extract, 

Grms. 


Protein, 
Grms. 


Protein, 

Grms. 


Fat. 
Grms. 


OxH: 
Period 5 
« 4 


Extracted straw. . 
Basal ration 

Starch 


116 
101 


3129 

1083 


3351 

2912 


654 
749 


157 

43 


735 
191 


Period 3 


15 

92 
101 


2047 

1057 
1083 


439 

4773 
2912 


-95 

629 
749 


114 

78 
43 


544 
565 


" 4 


Basal ration 

Extracted straw... 
Starch 


191 


Ox J: 
Period 5 
« 4 


-9 

110 
107 


-26 

3101 
1114 


1861 

3344 

2895 


-120 

747 
836 


35 

98 
33 


374 

693 
223 


Period 3 


3 

85 
107 


1987 

1105 
1114 


449 

4396 
2895 


-89 

764 
836 


65 

91 
33 


470 

472 


« 4 


Basal ration 

Difference 


223 




-22 


-9 


1501 


-72 


58 


249 



The varying quantities of nutrients digested stand in the way 
of a direct comparison of the results. If, however, we reckon 1 
gram of digested fat equivalent to 2.25 grams of digested crude 
fiber or nitrogen-free extract or protein (isodynamic quantities 
according to the usual method of computation), and if we further 
convert the gain of proteids into its equivalent amount of fat, on 
the same principle, by multiplication by 5.7 and division by 9.4, we 
have the results shown in the table on the opposite page. 

While no great quantitative accuracy attaches to such a com- 
putation, it is sufficient to show that the effect produced in this case 



THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 183 



Total 

Carbohydrate 

Equivalent 

of Nutrients, 

Grins. 



Total Fat 

Equivalent 

of Gain, 

Grms. 



Gain per 

Kilogram 

Nutrients, 

Grms. 



OxH: 

Extracted straw, period 5-4 . 
Starch, " 3-4. 

Ox J: 

Extracted straw, period 5-4 . 
Starch, " 3-4. 



2425 
1695 



2334 
1370 



613 
395 



509 

284 



252.8 
233.0 



218.1 
207.3 



by the addition to the basal ration of digestible matter five sixths 
of which was derived from crude fiber, was not inferior to that 
produced by the addition of an equal amount of pure starch. 

It would seem that these results may fairly be taken as showing 
that the products of the digestion of cellulose by ruminants are 
substantially of equal value with those of the digestion of starch. 
This, however, by no means warrants the conclusion that starch and 
cellulose are of equal value in ordinary feeding-stuffs. The mate- 
rial used in these experiments had been so altered mechanically 
and freed from incrusting materials by the treatment to which it 
had been subjected that 88.3 per cent, of its organic matter and 
95.8 per cent, of its crude fiber was digested. The same animals 
digested but 52.5 per cent, of the crude fiber of wheat straw, and 
the digestible organic matter of the latter proved far less efficient 
than that of either starch or extracted straw. A full discussion of 
these facts may be more profitably undertaken in connection with a 
consideration of the energy relations of feeding-stuffs in Part II; 
for the present it may suffice to point out that the difference just 
noted appears to depend on physical rather than chemical causes. 

Pentose Carbohydrates. — We have already (p. 156) seen reason 
to believe that the pentose carbohydrates may serve as a source of 
energy to the organism and protect other materials from oxidation. 
This, of course, is equivalent to an indirect production of fat. In 
the same connection, however, the experiments of Kellner, just 
mentioned, were referred to as indicating a direct participation by 
these bodies in fat production. About one third of the digested 
matter of the extracted rye straw was found to consist of bodies 



1 84 PRINCIPLES OF ANIMAL NUTRITION. 

yielding furfural, presumably pentosans, as appears from the follow- 
ing modified form of the last table : 





Total Carbohydrate Equivalent 
of Nutrients. 


Total Fat 
Equivalent 




Pentosans, 
Grms. 


Other Substances, 
Grms. 


of Gain, 
Grms. 


OxH: 

Starch, " 3-4 

Ox J: 

Extracted straw, period 5-4 

Starch, " 3-4 


809 
-34 

834 

-89 


1616 
1729 

1500 
1459 


613 

395 

509 

284 



If we regard the furfuroids as not contributing to the fat pro- 
duction, then we must assign to the other nutrients of the extracted 
straw a value from 66 to 74 per cent, greater than that of the 
digested matter of the starch, a result which is hardly conceivable. 
Apparently we must admit that the furfuroids in this case pro- 
duced approximately the same effect as the other non-nitrogenous 
nutrients and were at least indirectly if not directly a source of fat. 



CHAPTER VI. 

THE INFLUENCE OF MUSCULAR EXERTION UPON 
METABOLISM. 

It is a matter of common experience that muscular exertion 
results in a very marked increase in the vital activities of the body. 
The rate of circulation and respiration is greatly quickened and the 
increased metabolism in the organism is shown by the loss of weight 
and by the increased demand for food to make good the destruction 
of tissue. Indeed, no other factor even approaches muscular exer- 
tion in the extent to which it increases the metabolic activities of 
the body. 

We have now to. consider in some detail the nature of muscular 
exertion and the precise character of its effects upon metabolism. 

§ i. General Features of Muscular Activity. 

Muscular Contraction. 

The work of the muscles is accomplished by contracting, and a 
brief consideration of some of the more prominent general features 
of muscular contraction will conduce to an intelligent study of the 
main subject of the chapter. It will be possible here to consider 
this phase of the subject only in its most general outline, and the 
reader is referred to works on physiology for details. 

When a suitable stimulus, which in the living animal is usually 
a nerve stimulus, is applied to a muscle it contracts; that is, it 
tends to grow shorter and thicker. This change is brought about 
by a shortening and thickening of the individual fibers of which 
the muscle is built up. A single stimulus, such, for example, 
as that caused by the making or breaking of an electric circuit, 
gives rise to what is known as a simple muscular contraction. If 
such a stimulus is repeated with sufficient frequency it produces a 

185 



1 86 PRINCIPLES OF ANIMAL NUTRITION. 

series of simple contractions which fuse together, resulting in a state 
of contraction which continues, subject to the effects of fatigue, as 
long as the stimulus acts. This form of muscular contraction 
has received the name of "tetanus." In the living animal the 
ordinary contractions of the muscles brought about through the 
nervous system, even those that seem but momentary, are essen- 
tially tetanic in their character. 

Chemical Changes during Contraction.— Under the influence 
of a stimulus sufficient to produce a muscular contraction there 
occurs a sudden and large increase in the chemical changes which 
are continually going on even in the quiescent muscle. More mate- 
rial is metabolized in the muscle during contraction and energy is 
thus liberated for the performance of work. 

Our knowledge of the nature of these chemical changes in the 
contracting muscle is comparatively meager, but three main features 
appear well established: 

First, during contraction the neutral or slightly alkaline reac- 
tion of the quiescent muscle c" anges to an acid reaction, probably 
through the formation of sarcolactic acid. 

Second, there is a large increase in the amount of oxygen taken 
up by the muscle from the blood and a still greater increase in the 
amount of carbon dioxide given off by it.* 

Third, under normal circumstances, judging from the amount 
of the urinary nitrogen, there appears to be no considerable increase 
in the nitrogenous products of metabolism. 

From the increase in oxygen consumed and carbon dioxide given 
off we might be led at first thought to suppose that the increased 
activity in the muscle during contraction was of the nature of a 
simple oxidation. Certain other facts, however, seem to show that 
this view of the matter is inadequate. 

Oxidations Incomplete. — That the increased metabolism in 
the contracting muscle is not a simple oxidation of some material 
t carbon dioxide and water is indicated by the fact of the produc- 
tion of lactic or other acid in the muscle. Plainly, if the energy for 
muscular contraction is produced by oxidation the oxidation is at 
least incomplete. 

* Some good authorities doubt whether the carbon dioxide resulting 
from muscular exertion actually leaves the muscle in that form. Compare 
Schaffer, Text-book of Physiology, 1898, Vol. I, p. 911. 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 187 

Respiratory Quotient. — By analogy with investigations upon 
respiration we may designate the ratio between the oxygen con- 
sumed and the carbon dioxide given off by the muscle as the respi- 
ratory quotient of the muscle. Numerous investigations upon this 
point have shown that during contraction much more carbon diox- 
ide is given off than corresponds to the oxygen consumed, or, in 
other words, the respiratory quotient of the active muscle is con- 
siderably greater than unity. 

As early as 1862 Sczelkow * determined the gaseous exchange 
between the blood and the muscles of the posterior extremities of 
a dog, tetanus being produced by an electric current. He found 
that during rest more oxygen disappeared from the blood than 
corresponded to the carbon dioxide taken up by it, while during 
tetanus, on the contrary, the carbon dioxide considerably exceeded 
the oxygen. His results, calculated for the posterior extremities 
alone, were as follows: 



Experiment. 



1 

2 
3 
4 
5 



Rest . . . 
Tetanus 

Rest . . . 
Tetanus 

Rest . . 
Tetanus 

Rest . . . 
Tetanus 

Rest . . . 

Tetanus 



Per Minute. 



Carbon 

Dioxide 

c.c. 



1.60 
10.37 

2.62 

12.38 

1.73 
10.62 

3.53 
12.19 

2.33 
12.95 



Oxygen 
c.c 



4.10 
3.92 

4.25 

10.52 

3.21 
7.55 

4.71 
9.38 

5.82 
18.71 



Respiratory 
Quotient. 



0.41 
2.65 

0.62 
1.18 

0.54 
1.41 

0.75 
1.30 

0.40 
0.80 



In the above experiments, with a single exception, the quantity 
of oxygen consumed by the active muscles was more than that 
taken up in a state of rest, but the increase in the amount of carbon 
dioxide given off was still greater, so that the respiratory quotient 
was largely increased, exceeding unity in every instance but one. 



* Sitzungsber. Wiener Akad. d. Wiss., Math-Naturwiss. Klasse, 45, II, 171. 



PRINCIPLES OF ANIMAL NUTRITION. 



Chauveau & Kaufmann * have more recently obtained simi- 
lar results. Their experiments were made upon the Levator labii 
superioris of the horse, both in a state of rest and in a state of activ- 
ity consequent upon the consumption of food. From the amount 
and composition of blood entering and leaving this muscle the 
following results were obtained for the oxygen consumed and carbon 
dioxide given off per kilogram of muscle in one minute. On the 
average of the three experiments, in round numbers, twenty-one 
times as much oxygen was consumed during work as during rest and 
twenty-nine times as much carbon dioxide was given off. 





Oxygen Consumed. 


Carbon Dioxide Given Off. 


Experiment. 


Rest, 
Grms. 


Work. 
Grms. 


Work -f- 
Rest. 


Rest, 
Grms. 


Work. 
Grms. 


Work -=- 
Rest. 


2 


.00479 
.01167 
.00419 


.07148 
.20190 
. 14899 


14.9 
17.3 
35.6 


. 00365 
.01168 
.00518 


. 12534 
.35488 
.25709 


34.3 


3 


30 4 


4. .. 


49 6 






Average 


.00688 


. 14079 


20.5 


. 00864 


.24577 


28.5 



These facts show plainly that the increased metabolism of the 
active muscle cannot consist wholly of a direct oxidation, since the 
carbon dioxide given off from the muscle contains more oxygen 
than direct experiment shows to have been taken up by the muscle 
during the same time. 

Oxygen not Essential. — A further and still more striking 
proof of the above assertion is found in the fact that the living 
muscle can execute a considerable number of contractions in the 
entire absence of oxygen. 

Setschenow is quoted by Ludwig & Schmidt f as having found 
that muscles would contract freely when supplied with oxygen-free 
blood, while L. Hermann J has shown that an excised muscle may 
continue to contract in a vacuum. The well-known investigations 
of Pfliiger § show that frogs may continue to live and execute more 
or less extensive motions in an atmosphere of pure nitrogen for 

* Comptes rend., 104, 1126, 1352, 1409. 

f Verhandl. Sachs Akad. d. Wiss., Math-Phys. Klasse, 20, 12. 

% Unters. u. Stoffw. der Muskeln. 

§ Arch. ges. Physiol., 10, 313. 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 189 

several hours, giving out considerable amounts of carbon dioxide, 
and Bunge * has made similar observations upon the movements 
of certain intestinal worms (Ascaris) in one per cent, salt solution 
made as nearly oxygen-free as possible. 

Weinland t has shown that in the latter case the energy is 
derived chiefly from the cleavage of glycogen with the production 
of carbonic and valerianic acids. 

Summary. — The three classes of facts just adduced justify the 
conclusion that the chemical changes by which energy is liberated 
in a muscular contraction are not simply oxidations, but are of the 
nature of a cleavage of some complex substance or substances with 
evolution of carbon dioxide. There is, in other words, a sudden 
" explosive " decomposition of substances elaborated in the muscle 
during rest. Of the nature of the material thus broken down we 
have little definite knowledge. We can say, however, that if it is 
nitrogenous matter its nitrogen is ordinarily retained in the muscle 
in some form and that in effect the metabolized material is non- 
nitrogenous. The increase in the consumption of oxygen during 
work appears to be to a certain extent a secondary process, accom- 
plishing the further oxidation of the primary products of metabolism. 
At the same time, the fact that the amount of oxygen consumed 
responds very promptly to work and also to its cessation shows that 
these primary products, whatever they may be, are very speedily 
oxidized, either in the muscle or elsewhere in the organism. 

Thermal Changes during Contraction'.— A considerable por- 
tion of the energy set free during muscular exertion always takes 
ultimately the form of heat. When the muscle acts without shorten- 
ing, as when supporting a weight (isometric contraction) — that is, 
when no external work is done — all the metabolized energy takes 
the form of heat. If, on the other hand, the weight be lifted (iso- 
tonic contraction) — if external work is done — a portion of the 
energy takes the form of motion. The interesting question of the 
relation between the external work performed and the total amount 
of energy metabolized will be considered later. For the present it 
is sufficient to state that muscular action always produces heat 
and that a very considerable share of the metabolized energy 
ultimately takes this form. 

* Zeit physiol. Chem . 8, 48. f z eit. f. Biol., 42, 55. 



190 PRINCIPLES OF ANIMAL NUTRITION. 

Muscular Tonus. — The chemical and thermal changes just 
enumerated as characterizing the muscle during contraction are 
taking place in it to a less extent at all times. Even at rest the 
muscle respires and produces heat, as is well illustrated by Sczel- 
kow's and Chauveau & Kaufmann's experiments quoted above. 

The living muscles of the body are elastic and may be said to 
be always slightly on the stretch, as is shown by the fact that when 
cut they gape open and that they shorten when their attachments to 
the bones are severed. This slight degree of contraction of the resting 
muscles has been called muscular tonus, and it is at least a plausible 
conclusion that the chemical changes taking place in a quiescent 
muscle furnish the energy to maintain this tonus. According to 
Chauveau * we may regard the essence of muscular contraction as a 
sudden increase in the elasticity of the muscle. He holds that all 
the energy liberated by muscular metabolism is converted first into 
the elastic force of the muscle and only secondarily into heat. Ac- 
cording to this view the slight degree of elasticity of the quiescent 
muscle is produced by the constant metabolism going on within it. 
In active muscular contraction this process is greatly exaggerated 
and the katabolic processes exceed the anabolic, thus giving rise to 
a great increase in muscular elasticity which in turn may be con- 
verted into work. In repose following work, we may assume that 
the substances broken clown during contraction are built up again, 
while in prolonged repose the two processes must substantially 
balance each other. 

Muscular tonus is most noticeable during the waking hours, 
under the influence of external stimuli to the central nervous sys- 
tem, and consequently the rate of metabolism and the heat produc- 
tion tend to be greater than during sleep. To this is to be added, as 
a further cause of greater metabolic activity during the waking hours, 
those continual slight movements of the body which usually take 
place even in what is commonly spoken of as a state of rest and 
which may be designated as incidental movements. 

That the total amount of metabolism required for the mainte- 
nance of muscular tonus is considerable seems to be indicated by 
the observations of Rohrig & Zuntz,f and of Colasanti,J who 

* Le Travail Musculaire et l'Energie qu'il Represente. Paris, 1891. 
t Arch. ges. Physiol., 4, 57; 12, 522. % Ibid., 16, 157. 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM- 191 

found that when the motor nerves of the rabbit are paralyzed by 
curari the rate of metabolism, as measured by the respiratory ex- 
change, falls to about one half the amount during rest and does 
not react to changes of external temperature. Pfliiger * computes 
from his experiments a similar reduction of about 35 per cent. 
Under these conditions the heat production of an animal is insuffi- 
cient to maintain its normal temperature, and unless the loss of 
heat from the body is hindered by coverings or otherwise it soon 
perishes. Frank & F. Voit,f on the contrary, found that curarized 
dogs excreted no less carbon dioxide than in the normal state, pro- 
vided the body temperature was kept normal. 

Secondary Effects of Muscular Exertion. 

The greater activity of the muscular metabolism during the 
performance of work gives rise to important secondary effects, par- 
ticularly upon the circulation and respiration. It is a familiar fact 
that in active exercise the action of the heart is largely increased 
and the breathing becomes deeper and more rapid, and that ordi- 
narily the limit of muscular exertion is set, not by the power of the 
muscles themselves, but by the ability of the heart and lungs to 
keep pace with the demands upon them. 

Circulation. — The circulating blood is the medium by which 
oxygen is conveyed to the muscles and carbon dioxide and other 
products of their metabolism removed. The latter function is of 
special importance, since an accumulation in the muscle of the 
products of its own metabolism speedily reduces and ultimately 
suspends its power to contract. In active muscular exercise, there- 
fore, an increase in the rate of circulation is essential to the con- 
tinued activity of the muscles. This increase appears to be brought 
about by the accumulation in the blood of the products of metab- 
olism, which act as a stimulus to the vaso-motor center. The 
result is a dilation of the peripheral blood-vessels, which is aided by 
the mechanical effects of muscular contraction. To offset this and 
prevent a fall of arterial blood pressure, the visceral capillaries are 
probably constricted, while the rapidity and strength of the heart- 
beats are largely increased. The rapidity of the circulation as a 

* Arch. ges. Physiol., 18, 247. f Zeit, f. Biol., 42, 349. 



I9 2 PRINCIPLES OF ANIMAL NUTRITION. 

whole is thus greatly augmented, while at the same time a larger 
percentage of the total blood passes through the muscles. For 
example, in the experiments of Chauveau & Kaufmann, cited 
above, the ratio between the circulation in the resting as compared 
with the active muscle varied from 1 : 3.35 to 1 : 6.60. Zuntz & 
Hagemann,* in their investigations upon the work of the heart, 
found the average amount of blood passing through the heart of a 
horse per minute to be during rest 29.16 liters and during work 
53.03 liters. By this increase in the rate of circulation through 
the muscles the carbon dioxide and other injurious products of 
muscular metabolism are rapidly removed and an abundant supply 
of oxygen is ensured. In fact it is usually true that during work 
which is not excessive the venous blood contains less carbon diox- 
ide and more oxygen than during rest. 

Since the heart is a muscular organ, it is obvious that this in- 
crease in the circulatory activity must add materially to its metab- 
olism. In the performance of work, therefore, there is an expend- 
iture of matter and energy, not only for the work of the skeletal 
muscles but likewise for the additional work of the heart. Zuntz 
& Hagemann in their experiments upon the horse just mentioned 
compute that during moderate work the metabolism due to the 
work of the heart amounts to 3.8 per cent, of the total metabolism 
of the body. 

Respiration. — The greater activity of the circulation conse- 
quent upon muscular exertion would be futile were not provision 
made for more efficient aeration of the blood in the lungs through an 
increased activity of the respiration. The latter appears to be 
brought about, like the increase in the circulatory activity, by the 
effect of the greater amount of metabolic products in the blood, 
acting in this case upon the respiratory center. It has been shown 
that an accumulation of carbon dioxide in the blood does not have 
this effect, but that a lack of oxygen, such as occurs, for example, 
in asphyxiation, provokes powerful movements of the respiratory 
organs. In ordinary work, however, whatever may be the case in 
excessive muscular exertion, the effect is not caused by a lack of 
oxygen, for the blood, as already noted, is usually more arterialized 

* Landw. Jahrb., 27, Supp. Ill, 405. 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM- 193 

than during rest. Apparently the stimulation of the respiratory 
center is brought about by the other products of muscular metab- 
olism, whatever they may be, which find their way into the blood. 
Under the influence of this stimulus the respiratory movements 
increase in frequency or depth or both, thus making possible a 
more active gaseous exchange between the blood and the air in the 
lungs. This action is usually so efficient that the expired air dur- 
ing work contains a smaller proportion of carbon dioxide than it 
does during rest, notwithstanding the fact that the total quantity 
eliminated is much greater. 

Since respiration, like circulation, is maintained by muscular 
action, it is true in the former case as in the latter that a greater 
activity of the function necessitates a greater metabolism for 
that purpose. Zuntz & Hagemann * have recently investigated the 
work of respiration in the horse, the augmented respiratory activ- 
ity being brought about by an admixture of carbon dioxide to the 
inspired air, this resulting in a marked increase in the depth of the 
respiratory movements. With the animal upon which most of the 
experiments were made they found an increment of from 2.02 c.c. to 
5.23 c.c. of oxygen consumed for each increment of one liter in the 
volume of air respired. In general, although with some exceptions, 
the work of respiration as thus measured increased with the in- 
creased depth of the respiratory movements. The results upon 
other horses were somewhat variable. It was observed, however, 
that in the performance of ordinary work by the horse the effect 
was chiefly upon the frequency of respiration rather than its depth. 
The former effect the authors believe to involve less work than the 
latter and moreover an amount largely independent of the total 
volume of air respired. 

§ 2. Effects upon Metabolism. 

It is obvious from the foregoing paragraphs that the production 
of external work is a complex phenomenon. As regards its effects 
upon the total metabolism, the main features involved seem to be: 

1. An explosive decomposition of some unknown "contractile 
substance" in the muscles. 

* Landw. Jahrb., 27, Supp. Ill, 361. 



194 PRINCIPLES OF ANIMAL NUTRITION. 

2. The oxidation somewhere in the organism of the immediate 
products of this decomposition to the final excretory products. 

3. Since the state of contraction appears to be only an exagger- 
ation of the muscular condition during rest, we may reasonably 
suppose that there is a continual re-formation of the "contractile 
substance " going on. • 

4. As secondary effects there is a marked increase in the activ- 
ity of circulation and respiration, thus involving supplementary 
muscular exertion. 

It is plain that however interesting and important to the physi- 
ologist may be studies of the changes in the muscle itself, from 
the point of view of the statistics of nutrition the important thing 
is the total effect upon the expenditure of matter and energy by the 
organism under varying conditions of work. The energy relations 
of the subject will be discussed subsequently in Part II. Here we 
are concerned more particularly with the nature of the material 
expended in the production of work, and as a matter of convenience 
we may, as in the two preceding chapters, take up first the effect 
upon the proteid metabolism and second that upon the metabolism 
of the non-nitrogenous substances. 

Effects upon Proteid Metabolism. 

Earlier Investigations. — Since the muscles, which are the 
instruments by means of which work is produced, are composed 
essentially of proteid material, it was natural to regard the proteicls 
as the source of muscular power and to assume that the energy 
developed during work was supplied by an increased metabolism 
of these substances. This view was supported by the authority of 
Liebig, who, however, does not appear to have based it upon any 
actual experiments, and it was quite generally, although not 
universally, accepted. 

C. Voit * appears to have been the first to subject this idea to 
investigation. His experiments were made upon a dog weighing 
about 32 kilograms. The work performed, by running in a tread- 
mill, was considerable, being estimated to average 1.7 kgm. per 
second for the whole twenty-four hours. Experiments were made 
* Untersuchungen iiber den Einfluss des Kochsalzes, des Wassers, und 
der Muskelbewegungen auf den Stoffwechsel. 1860. Compare the summary 
by E. v. Wolff in Die Ernahrung der landw. Nutzthiere, pp. 386-388. 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM- 195 



both during fasting and with a daily ration of 1500 grams of lean 
meat. The results obtained were as follows: 



Number of 
Experiment. 


Meat 
Eaten, 
Grms. 




Water 
Drunk 
Grms. 


Urine 

Excreted, 

Grms. 


Urea 

Excreted, 

Grms. 


I 


•I 
"1 

1500 ] 
1500 1 


Rest 

Work 

Rest 

Work 

Rest 

Rest 

Work 

Rest 

Work 

Rest 


258 
872 
123 
527 
125 
182 
657 
140 
412 
63 


186 

518 

145 

186 

143 

1060 

1330 

1081 

1164 

1040 


14.3 


II 


16.6 
11.9 
12.3 


Ill 


10.9 
109.8 
117.2 


IV 


109.9 
114.1 
110.6 





The average increase of the proteid metabolism, as measured 
by the urea excreted, was in the fasting experiments 11.8 per cent, 
and in the experiments with food 4.95 per cent. The absolute 
difference in grams, however, was materially less in the fasting 
experiments, although approximately the same amount of work 
was performed in both cases. A similar experiment upon an 
older and quite fat dog while fasting showed an increase of only 
6 per cent, in the proteid metabolism. 

Subsequently Pettenkofer & Voit * made similar experiments 
upon a man, the work consisting in turning a heavy wheel provided 
with a brake. The work was performed in the respiration appara- 
tus. The results showed a large increase in the carbon dioxide 
excreted, but scarcely any effect was noted upon the excretion of 
nitrogen, as will be seen from the following table: 





Nitrogen 

of Urine, 

Grms. 


Carbon 

Dioxide 

Excreted, 

Grms. 


Water E 

In 

Urine, 
Grms. 


xcreted. 

Evapo- 
rated, 
Grms. 


Oxygen 

Taken Up. 

Grms. 


Number 

of 
Experi- 
ments. 


Fasting : 

Rest 


12.4 
12.3 

17.0 
17.3 


716 
1187 

928 
1209 


1006 
746 

1218 
1155 


821 
1777 

931 
1727 


• 762 
1072 

832 
981 


2 


Work 


1 


Average diet : 
Rest 


3 


Work 


2 







* Zeit. f. Biol., 2, 478. 



*9 6 PRINCIPLES OF ANIMAL NUTRITION. 

Pettenkofer & Voit regard the slight increase in the proteid 
metabolism which they observed in most cases as a secondary effect 
of muscular exertion. They have shown, as we have seen, that 
when the cells of the body are abundantly supplied with non-nitroge- 
nous nutrients, either in the form of food or of body fat, there is a 
tendency to diminish the proteid metabolism. In work, on the con- 
trary, large amounts of non-nitrogenous material are oxidized, as 
their respiration experiments show. The supply of these nutrients 
to the cells is thus diminished, and it is to this that they attribute 
the increase in proteid metabolism. 

Results like those just given can hardly be interpreted other- 
wise than as showing that the non-nitrogenous constituents of the 
body or of the food, rather than the proteids, are the source of the 
energy expended in muscular work, but the first attempt to com- 
pare the amount of work performed with the energy available from 
the proteids metabolized was the famous experiment of Fick & 
Wislicenus * in 1866. These observers made an ascent of the 
Faulhorn and found that the amount of proteids metabolized 
during and after the ascent, as measured by the urea excreted, was 
insufficient, according to their computations, to account for more 
than one third of the energy required to raise their bodies to the 
height of the mountain, making no allowance for the work of the 
internal organs, nor for those muscular exertions which did not 
contribute directly to the work done. 

Fick & Wislicenus found no considerable increase in the uri- 
nary nitrogen in their experiment. Subsequent investigators, 
among whom may be mentioned Parkes ; f Noyes,J Haughton,§ 
Meissner,|| Schenk,^[ and Engelmann,** have reported appar- 
ently conflicting results regarding the influence of work on the 
proteid metabolism. In some cases an increase was observed, 
while in other cases no material effect was apparent. The increase 
when observed was never large except in the experiments of Engel- 

* Vrtljschr. Naturf. Gesell. Zurich, 10, 317. 

t Phil. Mag., 4th ser., 32, 182. 

% Amer. Jour. Med. Sci., Oct., 1867. 

§ Brit. Med. Jour., 15, 22. 

|| Virchow's Jahresber., 1868, p. 72. 

If Centralb. Med. Wiss., 1874. p. 377. 

** Archiv f. (Anat. u.) Physiol., 1871, p. 14. 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 197 



mann, and was entirely insufficient to account for the energy ex- 
pended. Oppenheim made the interesting observation that work 
pushed to the point of producing dyspnoea caused a marked increase 
in the proteid metabolism. 

Influence of Total Amount of Food — Kellner's Inves- 
tigations. — Doubtless the conflicting results of earlier experiments 
are due in part to defective technique, but they arise in part also, 
as it would seem, from another cause to which attention was first 
called by Kellner in 1879-80. Kellner's experiments were made 
upon the horse. They differed from most earlier experiments, first, 
in that the comparison was made between different amounts of work 
instead of between work and rest, and second, that the individual 
periods instead of covering only a few days were extended over two 
or three weeks. 

Series I. — Kellner's first series * was made primarily for the 
purpose of testing the influence of work upon the digestibility of the 
food, but the total nitrogen of the urine was also determined. The 
methods employed for this purpose were somewhat imperfect, there 
being some mechanical loss and probably also a loss of ammonia 
from the urine, but the author believes the results of the several 
periods to be fairly comparable. The amount of work performed 
was measured by a dynamometer. The numerical results of the 
measurement have since been shown to be too high, but the relative 
amount in the several periods is not thought to be materially 
affected by this error. The results of the several periods are briefly 
summarized in the following table: 





Work, 
Kgm. 


Nitrogen. 


Live Weight 


Period. 


Digested, 
Grms. 


In Urine, 
Grms. 


of Period, 
Kgs. 


I 

II 

Ill 

IV 

V 


625,000 
1,250,000 
1,875,000 
1,100,000 

625,000 


134.41 
128.32 
132.72 
126.40 
129.41 


99.0 
109.3 
116.8 
110.2 

98.3 


534.1 
529.5 
522.5 

508.8 
518.0 



While the above figures show a considerable nitrogen deficit, 
the urinary nitrogen increased and decreased with the amount of 
* Landw. Jahrb., 8, 701. 



198 PRINCIPLES OF ANIMAL NUTRITION. 

work performed in a manner which can scarcely be explained other- 
wise than as a result of the changes in the latter. The ration con- 
sumed was amply sufficient for the light work of the first and fifth 
periods. When, however, more work was demanded from the 
animal, the live weight promptly fell off, showing that the total 
ration was insufficient. This insufficiency of the total ration Kellner 
believes to be the cause of the increase in the proteid metabolism. 

A consideration of the daily results confirms this view. In 
passing from periods of lighter to those of heavier work the increase 
followed promptly upon the change. . In Period III, with the most 
severe work, the proteid metabolism continued to increase through- 
out the period and apparently had not reached its limit at the 
close. Conversely, when the work was diminished in Periods IV 
and V it decreased as promptly as it had increased. Finally, it 
should be noted that the additional amount of proteids metab- 
olized was entirely insufficient to furnish an amount of energy 
equivalent to the increase in the work. 

In four succeeding series of experiments Kellner * has investi- 
gated this phenomenon more fully, some of the sources of error noted 
above having been avoided in the later researches. The results, as 
will appear, still show a deficit of nitrogen. Kellner estimates that 
about 6 grams of nitrogen per day were required for the growth of 
hoofs, hair, epidermis, etc., and believes that there was some loss of 
urinary nitrogen mechanically and chemically. 

Series II. — In this series of experiments the ration, consisting 
of 7.5 kilograms of hay and 4 kilograms of beans, was purposely 
made rich in protein. In spite of this liberal supply of protein, 
however, the same result as in the first experiment was noted to an 
even more marked extent. As in the first series, too, the increase 
in the excretion of nitrogen promptly disappeared when the amount 
of work was diminished. 

Series III. — In this series the animal was brought as nearly as 
possible into equilibrium with his food upon rather light work. The 
work was then trebled, while at the same time an addition was 
made to the non-nitrogenous ingredients of the ration by substitut- 
ing for a portion of the beans an amount of oats containing the same 
absolute quantity of protein. In this second period there was a 
slight increase in the digestibility of the protein and, therefore, a 
* Landw. Jahrb., 9, 651. 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 199 



■corresponding increase in the urinary nitrogen (compare Chapter 
V), but this was small compared with the much greater amount of 
work performed. Moreover, it did not, as in the first series of 
experiments, augment from day to day during the period of severe 
work. The following table shows the principal results of this 
series, the figures for urinary nitrogen and for live weight being 
given for the first and second halves of each period : 





Work, 
Kgm. 


Nitrogen. 


Live 


Period. 


Digested, 
Grms. 


In Urine, 

Grms. 


Weight, 
Kg. 


i :. 


810,000 

2,430,000 
810,000 


173.6 

178.8 
178.8 


j 158.9 
| 164.1 
j 174.0 
\ 174.8 
j 166.4 
| 171.4 


560.3 
556.8 
541.3 
539.7 
542 . 5 
543.3 


ii 


in 





Series IV. — Upon the basis of the foregoing facts Kellner deter- 
mined the maximum amount of work which his horse could perform 
on a fixed medium ration without causing an increase in the proteid 
metabolism. One kilogram of starch was then added to the ration 
and the maximum amount of work that could be performed upon 
this new ration without causing such an increase was determined. 
In the nature of the case this determination could not be of the 
highest accuracy, but it is amply sufficient for our present purpose. 
The principal results are given in the following table, the amount 
of work being expressed by the number of revolutions of the dyna- 
mometer, since relative results are all that are required: 







Work, 
Rev. 


Nitrogen. 


Live 


Period. 


Digested, 
Grms. 


In Urine, 
Grms. 


Weight, 
Kg. 


I 


r 

Without 
starch 

) With ) 
) starch \ 


300 
600 
600 
500 
400 

800 
600 


1 

y 121.1 - 

j 




107.2 
110.2 
115.6 
109.4 
109.6 

115.5 
109.6 


540.0 


Ha 


538.3 


lib 


533.1 


Ill 


532.5 


IV 


530.7 


I 


j- 120.1 | 


517.1 


II 


515.4 











PRINCIPLES OF ANIMAL NUTRITION. 



Kellner estimates that the maximum amount of work which 
could be performed on the ration containing starch was 700 rev- 
olutions as compared with a maximum of 500 revolutions without 
starch. Even if this estimate of Kellner's be regarded as high, it is 
evident from the figures given that the addition of the starch enabled 
materially more work to be performed without an increase in the 
proteid metabolism. The results obtained in this and the subse- 
quent series have been made the basis of interesting computations 
regarding the utilization of the potential energy of the food which 
will be considered in Part II. 

Series V. — This series was precisely similar to the preceding one, 
except that the addition of non-nitrogenous matter to the ration was 
made in the form of oil by substituting flaxseed for linseed meal. 
The protein of the ration remained unchanged, while the fat was 
increased by 203 grams. The results were entirely similar to those 
with starch, as the following table shows : 







Work, 
Rev. 


Nitrogen. 


Live 


Period. 


Digested, 
Grms. 


In Urine, 
Grms. 


Weight, 
Kg. 


la 


| Without [ 

> addition < 

of fat 

)■ addition \ 
of fat 1 


500 
500 
550 
550 

700 
700 
650 
650 


1 f 
[ 159.0 -! 

J 1 

1 f 

[ 153.9 -j 


148.9 
149.2 
147.5 
153.0 

148.1 
153.9 
145.6 
145.0 


496.5 


16 


493.2 


Ila 


485.8 


116 


479.4 


la 


476.0 


16 


469.0 


Ha 


466.4 


116 


460.8 







While Kellner's method of investigation may be regarded as 
somewhat imperfect and necessarily giving but approximate results, 
yet it suffices to bring out in a very striking manner the intimate 
relation existing between the supply of non-nitrogenous nutrients 
in the food of a working animal and the effect of the work upon the 
proteid metabolism. In conclusion, it should be noted that in 
all Kellner's experiments there was a fairly abundant supply of 
protein. Whether the same result would be obtained on a ration 
containing the minimum amount of proteids required by the organ- 
ism is not shown. In no case was the increase in the proteid metab- 
olism, when observed, sufficient to supply energy equivalent to the 
additional work done. 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 201 

Later Investigations. — In 1882 North * made experiments 
upon himself in which a considerable amount of work, mainly walk- 
ing from 30 to 47 miles while carrying a load of about 27 pounds, 
was performed on one day of each experiment. The account of the 
experiments does not give sufficient data for computing the total 
amount of work performed, but it was evidently very considerable 
and resulted in a marked increase in the excretion of nitrogen. It 
is not possible, however, to determine. whether the total food was 
adequate for the work days, but it was no greater then than during 
the periods of rest. 

Argutinsky,f in experiments upon himself, observed as a result 
of rather severe work a very marked increase in urinary nitrogen 
which continued at least three days after the cessation of the work. 
Munk I subsequently criticised Argutinsky's results on the ground 
that the supply of non-nitrogenous nutrients in his diet was insuffi- 
cient. Krummacher § obtained results quite similar to those of 
Argutinsky, but his experiments are open to the same criticism as 
those of his predecessor, namely, an insufficient supply of non- 
nitrogenous nutrients, as he himself points out in a later paper. 
Hirschfeldt | failed to observe any material increase in the nitrogen 
excretion as the result of work upon a diet containing a considera- 
ble excess of food over the amount required for maintenance. This 
was true both upon a diet containing little protein and one abun- 
dantly supplied with this nutrient. 

Pfliiger, like Liebig, regards protein as the sole source of mus- 
cular energy. As yet only a preliminary sketch of his investiga- 
tions has been published.^ He fed a lean dog upon prepared lean 
meat, that is, upon a nearly pure proteid diet, for seven months. 
The animal remained apparently in perfect health and was able to 
perform a large amount of work. Under the influence of the work 
the excretion of nitrogen was observed to increase somewhat, but 
not sufficiently to account for the energy expended in the work. 
This phenomenon Pfliiger explains by supposing that during work 

* Proc. Roy. Soc, 36, 14. 

t Arch. ges. Physiol., 46, 552. 

j Arch. f. (Anat. u.) Physiol., 1890, p. 552. 

§ Arch. ges. Physiol., 47, 454. 

II Virchow's Archiv., 121, 501. 

t Arch. ges. Physiol., 50, 98. 



PRINCIPLES OF ANIMAL NUTRITION. 



the organism economizes in its demands for proteids elsewhere than 
in the muscles. The further interesting observation was made that 
with continuous work the proteid metabolism, which at first showed 
an increase, diminished again and even reached its original value. 
With a ration containing but little protein and much non-nitrogenous 
material, a small increase of the proteid metabolism was observed 
as the result of work. The preliminary account of the experi- 
ments affords no adequate data for computing the sufficiency of 
the total food. 

Krummacher,* in his second investigation, made three separate 
experiments. In the first of these the total food was estimated to 
be approximately sufficient for maintenance (38 Cals. per kilogram), 
while in the other two it was much in excess of this. The following 
table shows the total amount of food per kilogram, expressed as 
Calories of metabolizable energy,t the amount of work performed, 
and the percentage increase of the proteid metabolism: 





Energy of Food. 


Work 

Measured, 

Kgm. 


Increase 
of Proteid 




Total. 
Cals. 


Per Kg. 
Weight. Cals. 


Metabolism, 
Per Cent. 


ExDeriment I 


2459 
5034 
5701 


38 
64 

72 


153,070 
324,540 
401,965 


21 


p « II...:...:.... 


22 


in 


7 







The work done consisted in turning an ergostat. It has been 
shown by subsequent investigators that not over 30 per cent, of 
the energy of the body material metabolized in the performance of 
work in this way can be recovered in the work actually done. 
Assuming this high figure, and further that Krummacher's esti- 
mate of the maintenance requirements is accurate, it appears that 
the food in these experiments was insufficient to supply the energy 
required for the amount of work actually done. 

It was observed, as in other experiments of this nature, that the 
increased excretion of nitrogen continued for a day or two after the 
cessation of the work. Only in the first experiment, however, was 
even the total proteid metabolism during the periods of work, to- 
gether with the excess above the rest value observed on succeeding 
* Zeit. f. Biol., 33, 108. t See Chapter X. 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 203 

days, sufficient to supply an amount of energy equal to that 
actually measured on the ergostat, so that at least the larger share 
of the energy must have been derived from non - nitrogenous 
materials. 

Zuntz & Schumburg,* in investigations upon soldiers, observed 
an increase of the proteid metabolism as the result of marching, 
carrying a considerable weight. The increase, however, seemed to 
bear no direct relation to the amount of work performed, but rather 
to the conditions under which it was done. Thus excessive heat or 
sultriness of the atmosphere, resulting in unusual fatigue, was ac- 
companied by an increased excretion of nitrogen. The increase 
continued during the two days following the work. 

Frentzel f experimented upon dogs. In the first series the ani- 
mals were fed pure fat, while in the second series no food was given. 
The work, which was done upon a tread power, was considerable. 
In the first series there was an increase of 9.25 per cent, in the nitro- 
gen excretion in the work experiments, while in the second series a 
maximum increase of 44.26 per cent, was computed, which, how- 
ever, is believed by the author to be too high. A method of com- 
putation which he considers more nearly correct makes the increase 
in the second period 13.31 per cent. In the first series of experi- 
ments the food consisted of 150 grams of fat per day except upon 
one of the work days, when only 80 grams were consumed. No data 
are given regarding the sufficiency of this ration, but according to 
E. Voit's compilation J it would appear hardly adequate for the 
maintenance of a dog of the weight used (36 kilograms). The work, 
therefore, even in the first series, was probably done upon insuf- 
ficient food. In neither case was the increase in the amount of 
protein metabolized equivalent in energy content to the actual 
amount of external work done, and in the first series even the total 
proteid metabolism was not, while if we allow for the consumption 
of energy in internal work, heat production, etc., it was not suf- 
ficient in either series. 

Atwater & Sherman § have reported observations upon the 

* Arch. f. (Anat. u.) Physiol., 1895, p. 378. 

t Arch. ges. Physiol., 68, 212. 

% Zeit. f. Biol., 41, 115 

§ U. S. Dept. Agr., Office of Experiment Stations, Bull. 98. 



204 PRINCIPLES OF ANIMAL NUTRITION. 

food consumption, digestion, and metabolism of three bicyclers 
during a six-day contest. They find that, in spite of an apparently 
liberal diet containing large amounts of protein, all three riders 
lost considerable proteid tissue during the race. The conditions of 
the investigation were not such as to permit of a determination 
of the sufficiency of the food consumed, but the computations by 
Carpenter of the actual amount of work done seem to render it very 
probable that the body fat must have been drawn upon to a con- 
siderable extent. 

Recapitulation. — The investigations above cited seem to show 
beyond a doubt that when work is performed upon food less than 
sufficient to maintain the body and supply the amount of energy 
required for the work the proteid metabolism is somewhat increased. 

Whether the converse of this is true, namely, that when the 
food is sufficient such an increase in the proteid metabolism does 
not occur, is not so clear, for the reason that in most, if not all, of 
the cases we have no adequate data as to the sufficiency of the 
food. It is plain, however, that the question is not so easily inves- 
tigated as might appear at first sight, and that the final solution of 
the relations of work to proteid metabolism can only be reached by 
means of investigations in which the total metabolism both of matter 
and energy is determined. 

Gain of Proteids during Work. — Caspari and Bornstein have 
recently made further investigations into the possibility of a gain 
of protein as a result of work which was mentioned above in con- 
nection with Pfliiger's experiments. 

Caspari * experimented upon a dog which received an amount 
of food computed to have been fully sufficient for its maintenance 
and to supply energy for the work clone. Furthermore, a consider- 
able portion of the non-nitrogenous nutrients of the ration, consist- 
ing largely of carbohydrates, was given shortly before the work was 
done, while in some cases additional sugar or fat was given at that 
time. In the first experiment, work was performed upon three 
successive days. Upon the second of these there was a consider- 
able increase of the urinary nitrogen, but upon the third its amount 
fell below that of the rest period. The average for the three days 
of work was almost exactly equal to the value found for the last 

* Arch. ges. Physiol., 83, 509. 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 205 

day of the rest period and less than the average for the four pre- 
vious rest days. 

In the second experiment the work was continued for four days, 
then a rest day intervened, and then the work was continued for 
five more days. At the outset there was a slight increase of the 
proteid metabolism, but in the second period of five days it showed 
a marked decrease resulting in a progressive gain of nitrogen by 
the body, as is shown in the following tabular statement of the daily 
average results: 



Day. 


External 
Work 
Done, 
Cals. 


Nitrogen 

of Food, 

Grms. 


Average 

Nitrogen 

of Feces, 

Grms. 


Nitrogen 

of Urine, 

Grms. 


Gain or 

Loss of 

Nitrogen, 

Grms. 


1- 5 

5- 7 

7- 8 








597 

467 

597 

596 



595 

590 

593 

588 

586 


25.11 
25.11 
25.11 
25.11 
25.11 
25.11 
25.11 
25.11 
25.11 
25.11 
25.11 
25.11 
25.11 


1.89 
1.89 
1.89 

1.78 
1.78 
1.78 
1.78 
1.78 
1.78 
1.78 
1.78 
1.78 
1.78 


23.68 

22.00 

21.98 

24.72 (?) 

23.32 

23.23 

21.83 

22.06 

20.82 

19 . 64 

20.39 

19.87 

19.79 


-0.46 
+ 1.22 
+ 1.24 


8-9 

9-10 


-1.39 

+ 0.01 


10-11 


+ 0.10 


11-12 

12-13 

13-14 

14-15 


+ 1.50 
+ 1.27 
+ 2.51 
+ 3.69 


15-16 


+ 2.94 


16-17 


+ 3.46 


17-18 


+ 3.54 







This gain Caspari ascribes to an actual growth of the muscles as 
the effect of exercise, this growth according to him taking the form 
of a hypertrophy of the fibers. No determinations of the gain or 
loss of carbon were made. 

Bornstein,* who had previously investigated the possibility of 
increasing the store of proteids in the body by the addition of pro- 
teids to the food, has also contributed to the investigation of this 
phase of the question. His experiments were made upon himself. 
For seven days he consumed a uniform ration containing a moder- 
ate amount of protein and sufficient non-nitrogenous nutrients, 
according to previous experience, to maintain his body. The latter 
was in equilibrium with the food as regards nitrogen from the first 
day. Then the proteid supply was increased by approximately 
50 per cent, by the ingestion of pure proteids and light work (17,000 
* Arch. ges. Physiol., 83, 540. 



206 PRINCIPLES OF ANIMAL NUTRITION. 

kgm. per day) done by turning an ergostat. As a result of the in- 
creased supply of proteids in the food the proteid metabolism in- 
creased promptly, reaching its maximum upon the fifth day, when 
it very slightly exceeded the supply. From that time, however, 
it decreased gradually during the remaining thirteen days of the 
experiment, so that a gain of proteids by the body resulted, which 
was still in active progress when the experiment was discontinued. 
Counting from the time when the proteid metabolism reached its 
maximum the average gain of nitrogen per day was 

First five days 1 . 28 grams 

Last five days 2.06 " 

Average of all 1 . 475 " 

The author computes that 22 per cent, of the proteids added to 
the food was stored up in the body. In a previous similar experi- 
ment without work it was found that only 16 per cent, was thus 
stored. 

Two respiration experiments with the Zuntz apparatus were 
made during the work. The difference between their results and 
those of similar experiments during rest was used as the basis for 
computing the actual amount of energy metabolized in the body for 
the performance of work. This was found to be equal to 0.0100875 
Cal. per kgm. external work, which is equivalent to 171.5 Cals. for 
the whole daily work of 17,000 kgm. Assuming the original ration 
to have been a maintenance ration, Bornstein computes that the 
portion of the added proteids which was actually metabolized was 
insufficient to supply the energy necessary for the work done and 
that some of the fat of the body was drawn upon. The loss in 
live weight was found to agree with this assumption. 

The above investigations seem to show, not only that work may 
be done without increasing the proteid metabolism but that it may 
actually result in diminishing it, a fact which appears in harmony 
with the common observation that the tendency of exercise is to 
build up the muscular tissue. 

Summary. — While the results which have been cited are not in 
all respects conclusive, and while further investigation is required 
to fully elucidate the relations of muscular exertion to proteid metab- 
olism, the following general conclusions seem to be justified by the 
evidence now available: 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 207 

1. The non-nitrogenous ingredients of the food or of the tissues 
are the chief source of muscular energy. In by far the greater 
number, if not all, of the experiments upon this subject the amount 
of protein metabolized, as measured by the nitrogen excretion, was 
insufficient to furnish energy equivalent to the work done, the de- 
ficiency being in many cases very great. This statement, it will be 
observed, does not assert that the proteids are not concerned in the 
production of this energy. We may regard it as very probable that 
the non-nitrogenous matter metabolized has first entered into the 
structure of the muscular protoplasm, which, as we know, consists 
largely of proteids, but in a contraction it is largely, if not wholly, 
the non-nitrogenous groups contained in the protoplasm which are 
metabolized rather than the nitrogenous groups. 

2. With insufficient food there may be a considerable increase 
in the proteid metabolism as a result of muscular exertion, espe- 
cially when pushed to exhaustion. 

3. This increase is far from sufficient to supply energy for the 
work actually done, is not usually proportional to it, and seems 
dependent to a considerable degree upon accompanying conditions. 

4. With sufficient food the increase of the total proteid metab- 
olism consequent upon muscular exertion is at the most slight and 
possibly equal to zero. 

5. In some cases a storage of proteids has been observed to 
result from the performance of work. 

Functions of Proteids. — If the above conclusions are admitted, 
it is possible to suppose that in a muscular contraction under favor- 
able conditions — that is, when there is an abundant supply of non- 
nitrogenous material — there is no increased metabolism of the 
proteids. This view of the subject would regard the question as 
being simply one of the relative supply of nutrients, the energy 
being evolved from non-nitrogenous nutrients when these are in 
abundance, while in default of them the proteids are drawn upon. 

Another view of the subject, however, is possible, and perhaps 
more probable. It would appear that muscular exertion tends to 
produce two opposite effects upon the proteid metabolism: first, 
to break down additional protein, as is shown when work is done 
upon insufficient food; and second, to build up proteid tissue when 



208 PRINCIPLES OF ANIMAL NUTRITION. 

the food is sufficient, as is illustrated in the experiments of Caspari 
and Bornstein. 

As a basis for a tentative hypothesis, it seems allowable to sup- 
pose that both these processes — that of anabolism and katabolism 
of proteids — are continually taking place in the muscle and that 
both are exaggerated by exercise. In other words, we may imagine 
that the performance of work by a normally developed muscle 
requires an increased proteid katabolism, which is balanced, at least 
in the course of the twenty-four hours, by a corresponding increase 
in the proteid anabolism. With a liberal supply of food proteids, 
then, a part of the latter would, during rest, simply undergo nitro- 
gen cleavage and be used virtually as "fuel," but when work was 
done they (or part of them) would be used to replace the proteids 
katabolized in the muscles. Upon this hypothesis, the proteids 
might play a not unimportant part in the production of muscular 
work without any evidence of it appearing in an increased nitrogen 
excretion. It is to be remarked, however, that even on this suppo- 
sition the proteids could not be regarded as furnishing all, or even, 
in many cases, a large share, of the energy liberated. On insuffi- 
cient food, the hypothesis would assume that the energy supply is 
deficient and that proteids which would otherwise be used for 
muscular anabolism are diverted to use as "fuel," probably under- 
going a preliminary nitrogen cleavage and furnishing their non- 
nitrogenous residue to the muscles as a source of energy. 

The above tentative hypothesis implies that if work were per- 
formed upon a ration containing only the minimum amount of 
proteids required during rest, it would cause an increase of the 
proteid metabolism, no matter how much non-nitrogenous mate- 
rial was supplied, because there would be no proteids available 
which could be diverted to repair the waste assumed to be occa- 
sioned by muscular activity. Up to the present time, however, 
we possess no experimental investigation of this phase of the ques- 
tion. 

However this may be, we know that the performance of work 
requires a well-developed muscular system. To produce and de- 
velop such a system, a liberal supply of protein is essential, while 
we may reasonably suppose that to maintain it involves a larger 
proteid supply in the food than is required to maintain the proteid 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 209 

tissue on a lower level. This fact alone would indicate the need of 
a reasonably liberal supply of protein in the food of working animals. 
If the hypothesis above outlined be approximately correct, it is 
necessary that the food also contain protein which during rest may 
be simply a source of heat, but which during work may be diverted 
to repair the increased waste of nitrogenous tissues caused by ex- 
ertion. This accords with the well-established fact that the dieta- 
ries selected by athletes and others who undertake severe physical 
exertion are almost invariably rich in protein.* It is of course 
difficult to say how far the large amount of proteids in the dietaries 
of athletes represents a real physiological demand and how far it is 
a matter of tradition or of taste, but it hardly seems likely that so 
universal an opinion should be lacking in some considerable basis 
of fact. 

Effects upon the Carbon Metabolism. 

In the foregoing paragraphs we have seen that as a rule the 
total proteid metabolism is not much affected by muscular exertion. 
While proteids undoubtedly have important functions in connection 
with the production of work, it is nevertheless true that normally 
the energy liberated in muscular contraction is derived chiefly or 
wholly from the breaking down of non-nitrogenous material. 
Moreover, even in those cases in which a considerable increase of 
the proteid metabolism has been observed, its amount has been 
entirely insufficient to account for the extra evolution of energy. 
It therefore becomes of especial importance to consider the effects 
of work upon the carbon balance. 

The Gaseous Exchange. — Since the influence of muscular ex- 
ertion upon the proteid metabolism is at most small, it is possible to 
compare the carbon metabolism during work and rest without 
material error upon the basis of the gaseous exchange simply, and 
as a matter of fact a large share of our knowledge of the subject 
rests upon determinations of the respiratory exchange. 

Is Largely Increased. — The fact that muscular work largely 
increases the evolution of carbon dioxide and water and the con- 
sumption of oxygen by the organism is too familiar from ordinary 

* For a summary of American experiments bearing upon this point see 
Atwater & Benedict, Boston Medical and Surgical Journal, 144, 601 and 629 



2IO 



PRINCIPLES OF ANIMAL NUTRITION. 



experience and too well established scientifically to require more 
than illustration. The fact of such an increase was shown in the 
researches of Lavoisier. Scharling,* who as early as 1843 con- 
structed an apparatus somewhat like the Pettenkofer respiration 
apparatus (see p. 70), states in his account of his experiments 
that moderate work increases the excretion of carbon dioxide and 
that it is also greater shortly after a meal. Of other early researches 
upon this point may be mentioned those of Hirn f in 1857, and 
especially those of Smith \ in 1859. The investigations of Petten- 
kofer & Voit § in 1866 appear to have been the first to be executed 
in accordance with modern methods. Their results have already 
been cited in their bearing upon the influence of work on proteid 
metabolism, but may be repeated here: 





Nitrogen 

of Urine, 

Grms. 


Carbon 
Dioxide 
Excreted, 

Grms. 


Water Excreted. 


Oxygen 

Taken 

Up. 

Grms. 


Number 
of Experi- 
ments. 




In 

Urine. 

Grms. 


Evapo- 
rated, 

Grms. 


Fasting : 

Rest 


12.4 
12.3 

17.0 
17.3 


716 
1187 

928 
1209 


1006 
746 

1218 
1155 


821 
1777 

931 
1727 


762 

1072 

832 
981 


2 


Work 


1 


Average diet: 
Rest 


3 

2 


Work 







Subsequent investigators such as Speck, || Hanriot & Richet,^" 
Katzenstein,** Loewy,ff and many others have fully confirmed the 
results of the early experimenters, The increase in the oxygen 
taken up was not actually demonstrated in all of these experiments, 
but it was in some and may be reasonably inferred in the remainder- 

* Ann Chem Bharm , 45, 214 

| Comptes rend Soc. de Physique de Colmar, 1857; Revue Scientifique, 
ler Semestre. 1887. 

\ Phil. Trans.. 1859, p 681. 

§ Zeit f Biol., 2. 478. 

II Schriften der Geselhder ges Naturwiss zu Marburg, 1871; Arch, klin 
Med., 45, 461. 

1 Comptes rend., 104, 435 and 1865; 105, 76; Ann. de Chim et de Phys.> 
(6), 22, 485. 

** Arch ges Physiol., 49, 330. 

tt Ibid, 49, 405. 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM- 211 



Effects are Immediate. — Experiments like those of Petten- 
kofer & Voit, extending over twenty-four hours, give simply the 
total effect of the performance of work upon the carbon balance. 
By the use of the Zuntz type of apparatus, however, it is possible 
to follow the gaseous exchange in its details through successive 
short periods as well as to determine the amount of oxygen con- 
sumed. The data thus obtained give a clear picture of the imme- 
diate effects of work upon metabolism and have led to the extensive 
use of this type of apparatus in experiments of this nature. The 
results of these experiments agree with common experience in 
showing that these effects appear very promptly and soon reach 
their maximum, disappearing as promptly after the work ceases. 
In other words, the increase in the carbon metabolism is very 
closely confined to the time during which the work is actually 
performed. 

The Respiratory Quotient. — The ratio between carbon dioxide 
produced and oxygen consumed, commonly known as the respira- 
tory quotient, as has been pointed out in Chapter III, enables us 
to form a fairly clear idea as to the general nature of the total mate- 
rial metabolized, and hence much study has been bestowed upon 
the relation between these two quantities. 

Is Variable.— We have already seen that the respiratory quo- 
tient may vary considerably during repose, being largely deter- 
mined by the nature of the food. The same thing is true of the 
respiratory quotient during work. 

Zuntz,* in experiments on a fasting dog, obtained the follow- 
ing values for this quotient: 



Number of 
Experi- 
ments. 


Average 
Respiratory- 
Quotient. 


2 


0.69 


6 


0.71 


8 


0.73 


5 


0.77 


10 


0.77 



Rest : Standing 

" Lying 

Horizontal locomotion 
Locomotion up hill. . . 
Horizontal draft 



In Zuntz & Hagemann's f experiments upon the horse the respi- 
ratory quotient in the single work periods ranged from 0.729 upon a 

* Arch. ges. Physiol, 68, 191. 

f Landw. Jahrb., 27, Supp. Ill, 296-331. 



212 PRINCIPLES OF ANIMAL NUTRITION. 

ration of green alfalfa to 0.996 upon hay, straw, and oats. The 
averages obtained for different forms of work were as follows: 

Walking, nearly horizontal . 865 

up a slight incline 0.847 

" " " steeper incline 0.900 

Draft, nearly horizontal 0.890 

Walking with load, horizontal . 840 

" up incline 0.893 

Trot, nearly horizontal . 882 

" with load, nearly horizontal . 873 

" horizontal draft 0.927 

The total range of the respiratory. quotient in these experiments 
was 0.84 to 0.93. It is thus seen to be higher with herbivorous 
animals, subsisting largely upon carbohydrates, than with the dog. 

Change Caused by Work. — Chauveau states as the result of his 
investigations upon the origin of muscular power that the per- 
formance of work always increases the respiratory quotient. 

His first experiments * were made upon a man who had fasted 
for sixteen hours. The work consisted in the alternate ascent and 
descent of a staircase, the work of ascending being equal to about 
29,000 kgms. in the seventy minutes of the experiment. Samples 
of the expired air were taken by the Tissot apparatus f for five 
minutes at a time at intervals during the work and the respiratory 
quotient determined by a comparison of its composition with that 
of the normal atmosphere. The following were the results for the 
respiratory quotient: 

Immediately before work . 75 

First to fifth minute . 84 

Tenth to fifteenth minute 0.87 

Fortieth to forty-fifth minute . 95 

Sixty-fifth to seventieth minute . 74 

♦Comptes rend., 122, 1163. 

f Archives de Physiol., 1896, p. 563. The apparatus is of the Zuntz type. 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM- 213 

A second experiment,* begun after fifteen hours' fasting, was 
divided into two periods. The first was similar to the previous 
experiment, but lasted for thirty minutes only, the work of ascent 
equaling in that time about 30,000 kgms. The subject then rested 
for a time during which he consumed 105 grams of butter. Two 
hours after the ingestion of the butter the experiment was repeated, 
samples of the expired air being taken for three minutes at a time. 
The results as regards the respiratory quotient were as follows: 

Fasting. 

Three minutes before beginning work 0.706 

Twelfth to fifteenth minute 0.804 

Twenty-seventh to thirtieth minute 0.812 

Rest 0.812 

Two Hours after Ingestion of Butter. 

Three minutes before beginning work . 666 

Twelfth to fifteenth minute. 0.783 

Twenty-seventh to thirtieth minute . 809 

In conjunction with Laulanie f he has also experimented on 
dogs and rabbits, the muscular contractions being caused by electric 
shocks. The method of determining the respiratory exchange, as 
described by Laulanie, consisted in using a Pettenkofer type of 
apparatus with a small but constant known rate of ventilation. 
The outgoing air passed through a small gasometer, but the current 
could be shunted and the sample of air contained in the gasometer 
analyzed. No details of the experiments or of the methods of cal- 
culation are given. The first table on the following page contains 
Laulanie's summary of the results. § 

An even greater increase in the respiratory quotient has been 
observed by other investigators. Thus Hanriot & Richet fl found 

* Comptes rend., 122, 1169 

t Ibid., 122, 1244, 1303: Archives de Physiol . 1896, p. 572. 

J Archives de physiol . 1896, pp. 619 and 636. 

§ Energetique Musculaire, p. 70. 

|| Comptes rend., 104, 435 and 1865; 105, 76. 



214 



PRINCIPLES OF ANIMAL NUTRITION. 





Food. 


No. of 
Expts. 


Respiratory Quotient. 




Before 
Work. 


During 
Work. 


After 
Work. 


Rabbit . . 


Ad libitum 


7 
5 

2 


0.880 
0.776 
1.016 


0.970 
0.849 
1.027 


799 


Dog ... . 


Fasting from 1 to 7 days .... 


733 


Dog ... . 


Abundantly fed with milk porridge . 


1.033 



in the increments of carbon dioxide and oxygen over the rest values 
quotients much greater than unity and reaching in one case 3.5 (?). 
Speck * likewise found an increase in the respiratory quotient as 
the result of work. Although he observed numerous exceptions, 
he regards it as the rule that it increases with the severity of the 
work. 

On the other hand, Katzenstein,f in experiments on men, found 
in some cases no considerable increase in the respiratory quotient 
during work. He gives the following average results, of which 
those in the first table do not relate to exactly the same subjects 
in the three cases : 

Turning Ergostat. 

Repose 0. 754 

Light work 0.824 

Heavy work 0.823 



Walking. 










Subject 
No. 1. 


Subject 
No. 2. 


Subject 
No. 3.* 


Subject 
No. 4. 


Repose 


0.801 
0.805 
0.799 


0.73 
0.77 
0.79 


0.77 
0.82 
0.865 


75 


Horizontal locomotion 


895 


Locomotion up hill 


86 







In all cases, the determinations of the respiratory exchange 
covered only a few minutes soon after the work began, and 



* Arch. klin. Med., 45, 461. 
t Arch. ges. Physiol., 49, 330. 
J A very corpulent individual. 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 215 

no mention is made of the nature of the diet except in one case 
(fasting). The individual results were rather variable, but most 
weight is given to those on Subject No. 1, with whom most of the 
•experiments were made. Katzenstein believes Speck's results to 
be due in part to a change in the rate of respiration, causing the 
-excretion of carbon dioxide to exceed its actual production (p. 73), 
and in part to a deficiency of oxygen in the tissue of the contracting 
muscles. 

Loewy,* like Katzenstein, found that work pushed to the point 
of producing a considerable degree of fatigue raised the respiratory 
quotient, while moderate work did not. Rapid turning of the 
wheel of the ergostat, preventing full breathing, or compression 
of the upper arm by means of a rubber band, produced the same 
effect, which he attributes to a lack of oxygen. The most marked 
results seem to be those for the first few minutes of work, although 
in one case work continued for ten to twenty minutes and producing 
fatigue raised the respiratory quotient. 

Probably the most extensive and carefully conducted investiga- 
tions of this nature are those of Zuntz and his associates upon the 
dog, and particularly on the horse. Some data from the latter 
investigations have already been given on p. 212. The following 
table adds to the averages there quoted those for the corre- 
sponding rest periods. In these experiments there was a distinct 
lowering of the respiratory quotient instead of an increase. In 



Kind of Work. 


Periods. 


Respiratory Quotient. 




Repose. 


Work. 


Walking nearly horizontal 

up slight grade 


a, b, e, f, i, 

a, b, e, 
a, b, e, f, i, n 

b, e, f, i 
e, i, 

e, i, 0, 
a, e, f, 

e, i, 

9,f,i 


0.943 
0.940 
0.953 
0.956 
0.915 
0.915 
0.943 
0.915 
0.943 


0.865 
847 


" steeper grade 


. 900 ' 


Draft, nearly horizontal 


0.890 


Walking with load, nearly horizontal. . . 

" up a grade 

Trot, nearly horizontal 


0.840 
0.893 

882 


with load 

" horizontal, with draft 


0.873 
927 







* Arch. ges. Physiol., 49, 405. 



2l6 



PRINCIPLES OF ANIMAL NUTRITION. 



all cases the animal was liberally fed, usually with oats, hay, and 
cut straw. 

Variation during Work. — In their experiments cited above, 
Chauveau & Laulanie find that the rise of the respiratory quotient 
which they regard as the invariable result of muscular exertion 
occurs promptly upon the beginning of the work, and the same thing 
is shown by the earlier results of Chauveau. As the work is con- 
tinued, however, the quotient shows a tendency to fall again, some- 
time even going below its original rest value, while in a period of 
rest following work a still further decrease is observed. The 
results of their experiments * are contained in the table on the 
opposite page. 

Zuntz & Hagemann f also report a number of experiments on 
the horse in which the respiratory exchange was determined in suc- 
cessive periods of work. The following are their results for the 
respiratory quotient: 



No. of 


Successive Values of Respiratory Quotient. 


Aggregate Length 
of Work Periods, 


Experiment. 


1 


2 


3 


Min. 


37 


.917 
.913 
.929 
.925 
.920 
.865 
.928 
.910 
.974 
.863 
.911 
.949 
.936 
.931 


.865 
.806 
.889 
.948 
.931 
.868 
.921 
.926 
.905 
.820 
.922 
.934 
.909 
.904 




80 


38 




897 
875 
911 

837 

!87i 

.878 
.883 


12H 


41 


102 


42 


100 


43 


92i 


45 


54 


46 


34 


47 


48 


58 

63 

66 

67 

78 


65 

73 

71 

124 

78 


96 


75 











The results cited in the foregoing paragraphs would appear to 
justify the general conclusion that in the case of fasting animals or 



* Comptes rend., 122, 1244. 
t Loc. cit., pp. 290-292. 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 217 






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2i8 PRINCIPLES OF ANIMAL NUTRITION. 

of those insufficiently fed the respiratory quotient is increased by 
the performance of work, while with well-fed animals, especially 
those receiving an abundance of carbohydrates, this effect is not 
apparent. As the work is continued, there appears in many cases 
to be a tendency toward a diminution of the quotient, while in rest 
following work a still further decrease may occur. 

Nature of Non-nitrogenous Material Metabolized. — As already 
pointed out, a comparative study of the final products of metab- 
olism during rest and work does not itself afford direct evidence 
as to the nature of the material actually metabolized in a muscu- 
lar contraction, but simply shows the total effect of the contraction 
itself and of the secondary activities resulting from it upon the 
make-up of the schematic body. When we attempt to go further 
than this, other methods of investigation are requisite, although 
experiments like those already cited may afford important con- 
firmatory evidence. 

Conclusions from Respiratory Quotient. — The significance 
of the respiratory quotient in experiments upon work has already 
been illustrated in Chapter III (p. 76). Neglecting any slight error 
due to small changes in the proteid metabolism, the variations in 
the respiratory quotient as outlined in the foregoing paragraphs 
enable us to trace the corresponding changes in the nature of the 
carbon metabolism. 

The metabolism of a fasting animal at rest is, as was shown in 
Chapter IV, largely a metabolism of fat. Corresponding to this, 
the respiratory quotient of such an animal approaches the value 
0.7 for pure fat, although never quite reaching it, since some pro- 
tein is always metabolized. Numerous instances of this fact are 
seen in the experiments already cited. When such an animal per- 
forms work, the respiratory quotient has been found to increase 
materially, thus showing that, in addition to the fat, carbohydrate 
material is being metabolized. This is entirely in accord with the 
well-established fact that muscular exertion causes the glycogen, 
both of the muscles and of the liver, to decrease and even disappear 
entirely. With an animal at rest and liberally supplied with car- 
bohydrate food, on the other hand, the respiratory quotient ap- 
proaches or even reaches unity, showing that the metabolism is 
essentially carbohydrate in character. When work is required of 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 219 

such a subject, little change is noted at first in the respiratory quo- 
tient. The cells of the body being richly supplied with carbohy- 
drates apparently utilize these as the most readily available source 
of energy. In either case, however, continued work makes large 
demands upon the non-nitrogenous materials available, the store 
of carbohydrates in the body is rapidly depleted, and the fat of the 
body is drawn upon to an increasing extent as a source of energy, 
the necessary result being a diminution in the respiratory quotient. 
In the experiments of Chauveau & Laulanie only the respira- 
tory quotients corresponding to the total metabolism are given, and 
consequently the changes in the character of the metabolism indi- 
cated above can only be traced qualitatively. In Zuntz & Hage- 
mann's investigations the increments of the carbon dioxide and 
oxygen over the rest values are given, and from them the propor- 
tion of oxygen applied respectively to the oxidation of fat and of 
carbohydrates is computed. The following average results for the 
various forms of work show clearly that the ratio of fat to carbo- 
hydrates metabolized may vary through a very wide range. 



Kind of Work. 


Periods. 


Oxygen per Minute 
applied to the Oxida- 
tion of 




Fat, 
c.c. 


Carbohy- 
drates, c.c. 


Walking nearly horizontal 


a, b, e, f, i, 

a, b, e, 

a, b, e, f, i, n 

b. e, f, i 
e,i,o 

6, i, 0, 
a,e,f,o 

e, i, 

9,f,i 


4.3638 
10.433 

8.665 
8.882 
5.962 
8.525 
7.852 
12:718 
14.007 


2 . 9962 


" up a slight grade 


7 465 


" " " steeper grade 


15.215 


Draft, nearly horizontal 


12 992 


Walking with load, nearly horizontal . . 
" up a grade 


3.317 
14. 892 




14 201 


" with load, nearly horizontal 

" " draft, horizontal 


16.023 
45 050 







The Intermediary Metabolism. — As stated, the conclusions 
drawn from the respiratory quotient relate, strictly speaking, to 
the total effect of muscular exertion upon the store of matter in the 
body. The results of such experiments show that, as a consequence 
of a given amount of work, a certain quantity of fat and of carbo- 
hvdrates has been oxidized somewhere in the organism. 



220 PRINCIPLES OF ANIMAL NUTRITION. 

Many eminent physiologists, however, notably Zuntz and his 
pupils, go further and regard both the fat and the carbohydrates of 
food or body tissue as immediate sources of muscular energy and as 
of value for this purpose in proportion to their content of potential 
energy — that is, to their heats of combustion. In other words, they 
hold that either fat or carbohydrates may be in effect directly 
metabolized by the muscular tissue and that each under like condi- 
tions yields substantially the same proportion of its potential energy 
in the form of mechanical work. 

On the other hand, Chauveau * and Seegen f and their followers, 
as has already been indicated, regard the carbohydrates as the im- 
mediate source of energy for all the vital activities and hold that fat 
(or proteids) must first be converted into dextrose by the liver before 
it can be utilized. It is particularly with regard to muscular exer- 
tion that this theory has been elaborated, the conclusions as to other 
forms of vital activity being to a considerable extent based upon 
analogy with the former. 

Functions of the Liver. — According to this theory the material 
which is actually metabolized in a muscular contraction is a carbo- 
hydrate, viz., either the dextrose carried to the muscle by the blood 
or the glycogen which is stored up in it. Muscular activity is thus 
brought into intimate relations with the sugar-forming function of 
the liver, and a chief office of that organ is considered to be the 
preparation of the necessary carbohydrate material from the various 
ingredients of the food. The main facts which have been estab- 
lished may be summarized as follows (compare Chapter II, §§ 1 
and 2) : 

1. Dextrose is being constantly formed by the liver, which not 
only modifies the carbohydrates of the food but likewise appears to 
produce dextrose from proteids and particularly, according to this 
school of physiologists, from fat. 

2. Dextrose is as constantly being abstracted from the blood by 
the tissues, particularly the muscular tissues, as is shown by the 
constancy of the proportion of dextrose in the blood. 

3. The dextrose content of the blood is, according to Chauveau, 

* La Vie et l'Energie chez l'Animale. 
| Die Zuckerbildung im Thierkorper. 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 221 

maintained during fasting until the very last stages of inanition. 
When it finally disappears there is a rapid fall in the body temper- 
ature and death speedily follows. 

4. Both the production of dextrose by the liver and its con- 
sumption in the tissues appear to be augmented by muscular exer- 
tion. 

The latter fact is shown by the well-known experiments of 
Chauveau & Kaufmann * upon the masseter muscle of the horse. 
Comparing the amount of blood passing through the muscle and 
the decrease in its percentage of dextrose in rest and in work they 
found that the consumption of dextrose in the two cases was in the 
proportion of 1 : 3.372. Subsequent experiments f upon the Leva- 
tor labii swperioris of the horse, the results of which as to the gaseous 
exchange have already been cited (p. 188), gave the following 
figures for the dextrose abstracted from the blood per kilogram of 
muscle in one minute : 





Rest, Grms. 


Work, Grms. 


Work -f- Rest. 


Experiment 2 

3 

4 


0.00598 (?) 
0.06358 
0.03976 (?) 

0.03644 


0.07026 (?) 
0.22303 
. 12852 


11.75 
3.51 
3 23 






Average 


0.14027 


3.85 







The authors also call attention to the fact that in these two 
series of experiments the arterial blood supplied to the active muscle 
contained a higher percentage of dextrose than that supplying the 
same muscle in a state of repose, notwithstanding the consumption 
of this substance by the muscle, and conclude that muscular activ- 
ity stimulates the production of dextrose by the liver. The observa- 
tion of Kulz,J that prolonged muscular exertion may cause the dis- 
appearance of glycogen from the liver, may perhaps be interpreted 
as sustaining this conclusion. 



* Comptes rend., 103, 974, 1057, 1153. 
f Ibid., 104, 1126, 1352, 1409. 
$ Arch. ges. Physiol., 24, 41. 



222 PRINCIPLES OF ANIMAL NUTRITION. 

Muscular Glycogen. — Especial interest attaches in this connec- 
tion to the behavior of the glycogen of the muscles. Nasse * 
appears to have been the first to show that the muscular glycogen 
is consumed during contraction. This result has been abundantly 
confirmed by other investigators, notably by Weiss,t while, as just 
stated, Kulz has shown that the same thing is true of the glycogen 
of the liver. 

It has also been shown that glycogen accumulates in muscles 
whose activity has been suspended by section of their nerves or other- 
wise. An early statement to this effect, unaccompanied by experi- 
mental proof, is by MacDonncl.J Chandelon § investigated the 
influence upon the glycogen content of the hind leg of a rabbit of, 
first, ligature of the arteries, and second, section of the motor nerves. 
The first treatment caused a large loss and the second a large gain 
of glycogen. Morat & Dufourt || confirmed these results and also 
found that the formation of muscular glycogen was more rapid in a 
fatigued quiescent muscle than in a normal one, while Aldehoff If" 
has shown that in a fasting animal glycogen persists longer in the 
muscles than in the liver and reappears first in the former when food 
is given. 

In view of these facts it can hardly be doubted that the muscu- 
lar glycogen is in some way a source of energy to the muscles, being 
destroyed during contraction and stored up again during rest. 

Chauveau's Interpretation. — By a comparison of their results for 
dextrose just cited on p. 221 with those for the gaseous exchange 
of the muscle as given on p. 188, Chauveau & Kaufmann show that 
during rest there was a storage of dextrose and of oxygen in the 
muscle. During work, on the contrary, more carbon dioxide was 
produced by the muscle than corresponded to the amount of dex- 
trose which was abstracted from the blood, and this carbon dioxide 
contained more oxygen than was supplied to the muscle by the 



* Arch. ges. Physiol , 2, 97; 14, 482. 

t Sitzungsber. Wiener Akad der Wiss., Math-Nat. Klasse, 64, II, 284. 

j Proc. Roy. Irish Acad., Ser. I, 7, 271. 

£ Arch. ges. Physiol , 13, 626. 

|| Archives de Physiol , 1892, 327 and 457. 

«I Zeit. f. Biol., 25, 137. 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 223 

blood during the same time. The average results, computed in 
milligrams per minute, were: 



During Rest, 
Mgrms. 



During Work, 
Mgrms. 



Oxygen from blood 

" in C0 2 produced 

" required to oxidize dextrose taken up from 

blood 

Carbon of C0 2 produced 

" " dextrose taken up 



0.11803 
0.08424 

0.58305 
0.03160 
0.21862 



2.48490 
3.15052 

2.35055 
1.18128 
0.88118 



During rest the muscle was storing up both carbohydrate (gly- 
cogen) and oxygen, thus supplying itself with a reserve of potential 
energy. During activity this reserve, as well as the supply brought 
by the blood, was drawn upon for the performance of work. 

The fluctuations of the respiratory quotient resulting from mus- 
cular exertion are explained by Chauveau in outline as follows : 

At first there is a rapid oxidation of the stored glycogen of the 
muscles and of the dextrose of the blood, resulting in a respiratory 
quotient approaching unity. As the work progresses the store of 
carbohydrate material in the organism becomes relatively exhausted, 
unless there is a large supply of it in the food, and to meet the 
demands of the muscles an increased production of dextrose from 
the fat of the food or of the body takes place in the liver. This 
change, however, according to the equation proposed on p. 38, con- 
sumes 67 molecules of oxygen for each 18 molecules of carbon diox- 
ide produced. This process, superadded to the combustion of 
carbohydrates in the muscles, results in the observed lowering of 
the respiratory quotient. The further lowering of the quotient 
during a succeeding rest period results from the great diminution 
in the amount of carbohydrates oxidized in the muscles, the for- 
mation of carbohydrates from fat in the liver still continuing 
for a time in order to replenish the exhausted store of muscular 
glycogen. 

Fat as a Source of Muscular Energy. — According to the above 
theory, fat is only indirectly a source of muscular energy, in 
that it serves for the production of dextrose in the liver, and the 



224 PRINCIPLES OF ANIMAL NUTRITION. 

same thing is held to be true of protein so far as it contributes 
energy for muscular exertion. 

As we have seen in Chapter II, however, the formation of dex- 
trose from fat in the liver is by no means universally admitted, and 
Chauveau's ingenious theory as to the immediate source of muscu- 
lar energy has not lacked opponents. If it is true, fat has a much 
lower value for that purpose than corresponds to its potential 
energy as measured by its heat of combustion. If it be assumed 
to be converted into dextrose in accordance with the equation on 
p. 38, it is easy to compute that about 36 per cent, of its potential 
energy will be liberated as heat in the process and that consequently 
only the 64 per cent, remaining in the resulting dextrose will 
be available to the muscles. Consequently the relative values of 
fat and dextrose for the production of work will be as 162 to 100 
and not as 253 to 100. 

While the evidence of the respiratory quotient is not incon- 
sistent with Chauveau's theory, it is also not inconsistent with the 
view which supposes fat to be directly metabolized for the produc- 
tion of mechanical work. The difference lies, not in the amounts 
of carbon dioxide and oxygen evolved but in the place where and 
the form in which the energy is liberated, and the question can 
therefore be satisfactorily discussed only on the side of its energy 
relations. 

Postponing that discussion for the present, it may be remarked 
here that while it appears to be true, as already stated, that the 
muscular glycogen and the dextrose of the blood are a source of 
muscular energy, and perhaps the most readily available one, it 
by no means follows that they are the only source. The muscle 
contains other non-nitrogenous reserve materials besides glycogen, 
and notably a not inconsiderable amount of fat and of lecithin. 
Moreover, recent investigations (see pp. 63 to G5) have shown that 
the amount of the muscular fat is greater than was formerly sup- 
posed, and that some of it cannot be extracted with ether and 
behaves almost as if in chemical combination. Indeed, it appears 
not improbable that both fat and carbohydrate molecular groupings, 
as well as proteids, enter into the structure of living protoplasm. 
Finally, not only the muscle but the blood which nourishes it 
contains fat as well as carbohyhrate's, the former indeed being more 



INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM- 225 

abundant than the latter. There would seem to be no inherent 
difficulty, then, in supposing that the fat of the muscle and of the 
blood serves directly as a source of energy, although the writer is not 
aware of any investigations upon the influence of the contraction 
,of a muscle upon its fat-content. 



PART II. 
THE INCOME AND EXPENDITURE OF ENERGY. 



CHAPTER VII. 
FORCE AND ENERGY. 

Force is defined as whatever is capable of changing the rate of 
motion of a mass of matter. When a force acts upon a mass, im- 
parting to it a certain velocity, it does work, the amount of work 
being measured by the product of the force into the distance through 
which it acts. Energy may be defined as the capacity to do work. 
Any mass of matter which can act upon another mass in such a 
way as to change its rate of motion is said to possess energy. 

Kinetic and Potential Energy. — In studying energy we 
distinguish between kinetic energy, or the energy due to motion, 
and potential energy, or the energy due to position. The falling 
weight of a pile-driver at the instant it strikes the pile possesses a 
certain amount of kinetic energy and does a corresponding amount 
of work on the pile. When it is raised again a certain amount of 
work is done on it, and when it comes to rest at the top of the ma- 
chine a corresponding amount of energy is stored up in it as poten- 
tial energy. As long as the weight is supported at this point it 
does no work, but simply possesses the possibility of doing work. 
When it is allowed to fall again, this potential energy due to its 
position is converted into the actual or kinetic energy of motion, 
and when it reaches the point from which it was raised and strikes 
the pile it does work upon the latter exactly equal to that formerly 

226 



FORCE AND ENERGY. 227 

stored up in the weight as potential energy, which again was equal 
to the energy expended in raising it. 

An even simpler example of the conversion of potential into 
kinetic energy and vice versa is a swinging pendulum. When at 
rest for an instant at the end of a vibration it possesses a certain 
amount of potential energy, corresponding to its vertical height 
above the lowest point of its arc. When it reaches this lowest 
point, so far as the mechanism of which it forms part is concerned 
it has no more potential energy because it cannot fall any farther. 
In place of this, however, neglecting mechanical resistances, it con- 
tains an exactly equivalent amount of kinetic energy, due to its 
motion. During the second half of the swing this kinetic energy 
is expended in again raising the pendulum, and when it has all been 
expended the pendulum will (in the absence of external resistance) 
have been raised to exactly the same height as before above its 
lowest point. In other words, its kinetic energy will have been re- 
converted into an equivalent amount of potential energy and so 
the alternate conversion and re-conversion goes on as long as the 
pendulum continues to swing. 

The same facts which have been illustrated above in the case of 
the motion of visible masses of matter are likewise true of molecular 
and atomic motions. When molecules of carbon dioxide and water 
are converted into starch in the green leaves of the plant, work is 
done upon them by the energy of the sun's rays. Their constituent 
atoms are forced apart and compelled to assume new groupings. In 
this process a certain amount of kinetic energy has disappeared 
and the resulting system of starch molecules and oxygen molecules 
contains a corresponding amount of potential energy. Under 
suitable conditions the reverse process may also take place. The 
atoms may, so to speak, fall together and resume their old positions, 
producing the original amounts of carbon dioxide and water and 
giving off in the process the exact amount of kinetic energy which 
was originally absorbed. This energy may appear in the form of 
heat, as in ordinary combustion, or in any other of the various 
forms of energy, according to circumstances. 

The last example is but an illustration of the general fact that 
in every chemical reaction there occurs a transformation of energy 
which most commonly takes the form of an evolution or absorption 



228 PRINCIPLES OF ANIMAL NUTRITION. 

of heat. That branch of science which deals with the connection 
between chemical and thermal processes is known as thermo-chem- 
istry. Since kinetic energy in the animal is derived from chemical 
processes, and since it largely takes the form of heat, we may regard 
the study of the transformations of energy in the organism as con- 
stituting a branch of thermo-chemistry and proceed to a consider- 
ation of the fundamental laws upon which the latter subject is 
based. 

The Conservation of Energy. — In any system of bodies not 
acted on by external forces the sum of the potential and kinetic 
energy is constant. In other words, while the ratio of potential 
to kinetic energy may vary, and while each may take various forms, 
as mass-motion, heat, electric stress, etc., there is no loss of energy 
in these conversions. Energy, like matter, is indestructible. This 
great law of the conservation of energy was first clearly enunciated 
by Mayer, and forms the foundation of all modern conceptions of 
physical processes. In the case of the swinging pendulum used 
above as an illustration the total energy of the system composed 
of the earth and the pendulum is constant, a portion of it simply 
alternating between the potential and kinetic states. So, too, in 
the system of atoms of carbon, hydrogen, and oxygen, the potential 
energy contained in the system before the starch is burned is simply 
converted into the kinetic energy of heat, while the total energy 
of the system remains the same. 

Initial and Final States. — An important consequence of the 
law of the conservation of energy, which was first deduced and 
demonstrated experimentally by Hess in 1840, is known as the law 
of initial and final states. This law is that in any independent 
system the amount of energy transformed from the potential to 
the kinetic form, or vice versa, during any change in the system, 
depends solely upon the initial and final states of the system and 
not at all upon the rapidity of the transformation or upon the kind 
or number of the intermediate stages through which it passes. 
Although this law is true in the general form here stated, it was 
originally propounded as related to chemical reactions and forms 
the basis of the science of thermo-chemistry. If we start with 
starch and oxygen and end with the corresponding quantities of 
carbon dioxide and water, the amount of kinetic energy evolved is 



FORCE AND ENERGY. 229 

the same, no matter whether the starch be burned almost instanta- 
neously in pure oxygen or whether it be subjected to slow oxidation 
in the tissues of a plant buried in the soil; whether carbon dioxide 
and water are the immediate products of the action or whether the 
starch be previously transformed into maltose, glycogen, dextrose, 
lactic acid, etc., etc., as in the body of the animal. We have simply 
to determine the potential energy of the system in its initial and in 
its final state, and the difference is equal to the amount of kinetic 
energy evolved during the change. The truth of this law, as ap- 
plied to chemical processes, has been fully demonstrated by the 
researches of Berthelot and Thomsen. That the same law applies 
to the processes taking place in the body of the animal is exceed- 
ingly probable, a 'priori, and has been demonstrated experimentally 
by the researches of Rubner and of Atwater and his associates. 

Heats of Combustion. — We have no means of determining 
the total amount of potential energy contained in a system, but can 
only measure that portion which is manifested by the change to 
the kinetic or the potential form during some change in the system. 
In other words, we may assume the potential energy of the system 
in some particular state as zero and obtain a numerical expression 
for its potential energy in some other state as compared with this 
standard state. For the latter we shall naturally select that one in 
which no further conversion of potential into kinetic energy can, 
according to our experience, take place. 

In the case of organic substances, such as those entering into 
the metabolism of the animal, the system consists of the substance 
itself and oxygen, and the state of complete oxidation is the one in 
which experience shows that no further evolution of kinetic energy 
is possible by chemical means. Thus, to recur to the example of 
starch, if one gram be oxidized in accordance with the equation 

C e H 10 O 5 + 60 2 = 6CQ 2 + 5H 2 0, 

the amount of heat evolved will be 4183 cals.,* this being the amount 
of energy converted from the potential to the kinetic form. From 
the system represented by the second member of the above equa- 
tion we can get no further evolution of heat. We therefore repre- 

* For the units of measurement see the following paragraph. 



230 PRINCIPLES OF ANIMAL NUTRITION. 

sent its potential energy by and accordingly that of the system 
starch + oxygen by 4183 cals. for each gram of starch. This value 
is called the heat of combustion of starch, and shows how much 
energy can be liberated from this substance by its conversion into 
C0 2 and H 2 0. It is common to speak of this as the potential energy 
of the starch, and the expression has the advantage of brevity, 
but it should not be forgotten that it is really the potential energy 
of the system C 6 H 10 O 5 + 60 2 as compared with the system 
6C0 2 + 5H 2 0. 

In like manner the heat of combustion of any organic com- 
pound, or of any mixture of compounds such as a feeding-stuff, 
represents the amount of energy which a given weight of it evolves 
in the form of heat when completely oxidized. In the case of 
nitrogenous bodies the final products are C0 2 , H 2 0, N 2 , and in 
case of proteids S0 3 . 

Heats of combustion may be determined at constant pressure 
or at constant volume. When the substance is burned under ordi- 
nary atmospheric pressure the amount of heat evolved may include, 
besides that due to the difference in the chemical energy of the 
substance before and after burning, a mechanical component due 
to the fact that the volume of the products is not the same as that 
of the original substances. If it is greater, work is done in 
overcoming atmospheric pressure and the heat production is 
diminished by a corresponding amount. In the contrary case, work 
is done by the atmosphere upon the products of combustion and 
heat is evolved. When the substance is burned in a confined 
volume of oxygen, as in the bomb-calorimeter, the possibility of 
such mechanical action is eliminated and we obtain a quantity of 
heat representing solely the difference in chemical energy. The heats 
of combustion at constant volume are therefore, from a theoretical 
point of view, the more correct. On the other hand, however, all 
ordinary processes of combustion, including those occurring in the 
animal organism, take place under atmospheric pressure, which is 
practically constant, and therefore the actual heat value of a sub- 
stance oxidized in the body is measured by its heat of combustion 
at constant pressure. If there is no change in volume during the 
combustion, then the two heats of combustion are, of course, iden- 
tical. This is the case, for example, with the carbohydrates, which 



FORCE AND ENERGY. 231 

form so large a part of the food of herbivorous animals. Further- 
more, the difference in the case of the other common nutrients is so 
slight that the heats of combustion as determined with the bomb- 
calorimeter may be used without appreciable error in computing 
the metabolism of energy in the body. The only substance involved 
in such computations for which the correction needs to be made is 
methane, CH 4 , the heat of combustion of which is at constant 
volume 13,246 cals. per gram and at constant pressure 13,344 cals. 

Units of Measurement. — The unit of force is the dyne, which 
is defined as the amount of force required to produce in a mass of 
one gram, in one second, an acceleration of one centimeter per 
second. 

When a .orce acts upon a mass, the amount of work done is 
measured by the product of the force into the distance (measured 
along the direction of the force) through which it acts. The unit 
of work is the erg, which is defined as the work done by a force of 
one dyne acting through one centimeter. 

Energy has been defined as the power of doing work, and is 
measured by the amount of work done, that is, in ergs. Since, 
however, the erg is a very small quantity, it is often more con- 
venient in practice to use a multiple of it. For this purpose the 
quantity 10 10 erg=l Kilojoule (J) is a convenient unit. Energy is 
also frequently expressed in units based on weight instead of mass, 
the most common being the gram-meter, the kilogram-meter, and 
the foot-pound. The gram-meter is the work done against gravity 
in raising a weight of 1 gram through 1 meter. Since, however, the 
force of gravity, and consequently the weight of a given mass, varies 
at different points on the earth's surface, it is necessary to state 
also where the weight is taken. At the level of the sea, in temperate 
latitudes, the force of gravity equals 980.5 dynes. Under these 
conditions, then, doing 1 gram-meter of work would be equivalent 
to exerting a force of 980.5 dynes through 100 cm., which equals 
98,050 ergs. The kilogram-meter (kgm.) is the work done against 
gravity in raising 1 kilogram through 1 meter, and is accordingly 
1000 times the gram-meter or 98,050,000 ergs. The foot-pound 
is the work done against gravity in raising 1 pound through 1 foot 
and accordingly equals 13,550,000 ergs. 

In addition to mechanical energy the animal produces heat. 



232 PRINCIPLES OF ANIMAL NUTRITION. 

For the measurement of heat various units are in use, but the ones 
most commonly employed in physiology are the small and the large 
calorie. The small calorie (cal.) is defined as the amount of heat 
required to raise the temperature of 1 gram of water through 1° C. 
Since, however, the specific heat of water varies somewhat with the 
temperature, it is necessary to specify the average temperature 
of the water. The temperature of 18° C. has been quite commonly 
used for this purpose, the resulting unit being indicated by the 
abbreviation cal 18 . Atwater & Rosa,* however, in their work 
with the respiration-calorimeter, have employed the temperature 
of 20° C, designating their unit by cal 20 . The difference between 
the two is very slight, 1 cal 20 equaling 1.0002 cal 18 . The large 
calorie (Cal.) is the amount of heat required to raise the tempera- 
ture of one kilogram of water through 1° C, or is equal to 1000 small 
calories. The temperature at which the large calorie is measured 
may be indicated as in case of the small calorie. 

The calorie, however, while commonly used, and while in some 
respects a convenient unit, is in a sense not a rational one. Since 
heat is one form of energy, and since, in accordance with the law of 
the conservation of energy, there is a fixed relation between it and 
other forms of energy, a rational unit would be one bearing a simple 
numerical relation to the units employed to measure other forms 
of energy, or in other words, the erg or some simple multiple of it. 
As already noted, the Kilojoule (J) is a convenient unit for this 
purpose. It has two advantages over the Calorie : first, it permits 
of a direct comparison of heat with other forms of energy (expressed, 
of course, in units of the same system) ; and second, it is an " abso- 
lute" unit, that is, it is based on the fundamental units of space, 
mass, and time, and has a perfectly definite magnitude, while the 
Calorie has not unless the temperature at which it is measured is 
stated. To this may be added that in discussing physiological 
relations it avoids the sometimes confusing implication that the 
quantities of energy dealt with actually exist in all cases as heat. 

The relation between the Calorie and the Kilojoule is as follows: 

lCal 18 = 4.183 J =41,830,000,000 ergs; 
U = . 2391 Cal 18 = 10,000,000,000 ergs. 

* U. S. Dept. Agr., office of Expt. Stats., Bull. 63, p. 55. 



FORCE AND ENERGY. 



2 33 



Since, however, most of the results of investigations upon the 
physiological relations of energy are expressed in calories (often 
without any statement of temperature) it will be more convenient 
in the following pages to employ this unit rather than the more 
rational Kilo joule. 

Finally, since measurements of mechanical energy (as in experi- 
ment* with working animals) have been commonly made in weight 
units, it is necessary to know the relation of these to the calorie. 
These relations are included in the following table, the force of 
gravity being taken as 980.5 dynes: 



EQUIVALENCE OF UNITS OF ENERGY. 





Ergs.* 


Kilojoules. 


Gram- 
meters. 


Kilogram- 
meters. 


1 Kilojoule = 


10 10 
980.5X10 2 
980.5X10 5 
135.5X10 6 
4.183X10 7 
4.183X10 10 




101989 

1000 

138.2 

426.6 

426600 




1 gram-meter = 

1 kilogram-meter = . . . . 

1 foot-pound = 

1 cah 8 


980.5-hIO 8 
980. 5 -=- 10 5 
135.5-r-lO 5 

0.004183 

4.183 


0.001 

0.1382 
0.4266 


1 Calis 


426.6 







1 Kilojoule = . . . 
1 gram-meter = , 
1 kilogram-meter 
1 foot-pound = .. 

1 call « 

1 Cal.a 



Foot- 
pounds. 



738.1 
0.007236 
7.236 



3.087 
30S7. 



calu 



239.1 
0.002344 
2.344 
0.3239 



1000 



Call. 



0.2391 

0. 2344 h- 10* 

0.002344 

0.000324 

0.001 



* From Ostwald, Grundriss der allgemeinen Chemie. 



CHAPTER VIII. 
METHODS OF INVESTIGATION; 

The food is the sole known source of energy as well as of matter 
to the body of the warm-blooded animal, and the total income of 
potential energy, according to the principles laid down in the pre- 
ceding chapter, is represented by the heat of combustion of the 
food. 

A portion of this food, as we have seen in Part I, is metabolized 
in the body, while part of it escapes complete oxidation and is re- 
jected as undigested matter in the feces, as metabolic products in 
feces, urine, and perspiration, and as combustible intestinal gases. 
All these substances still contain more or less of their original store 
of potential energy and collective!}' constitute one main division of 
the outgo of energy. We may call it, for brevity, the outgo of 
potential energy. A portion of the food may also be applied to the 
production and storage of tissue (protein and fat) in the body, and 
this, from our present point of view, is to be classed with the 
outgo of potential energy. 

The potential energy of the remaining portion of the food, viz., 
that which is completely oxidized, may take various transitory 
forms in the organism, but ultimately it leaves it in one of two 
forms of kinetic energy, viz., as mechanical work or as beat. Here 
we have the second main division of the outgo of energy, viz., the 
outgo of kinetic energy. These relations may be briefly expressed 
in tabular form, as shown at the head of the opposite page. 

As in the corresponding chapter of Part I, it is proposed to con- 
sider here simply the general principles of the more important 
methods available for determining the income and outgo of poten- 
tial and kinetic energy, without entering into technical details. 

234 



METHODS OF INVESTIGATION. 235 



Income : 

Food 
Outgo : 

Feces 

Urine 

Perspiration 

Combustible gases 

Storage of tissue 

Work 

Heat 



Potential energy. 



r Kinetic energy. 



Determination of Potential Energy. 

The Energy of the Food. — The potential energy of the food is 
conveniently measured by converting it into the kinetic form of heat; 
that is, by determining its heat of combustion. This determina- 
tion is effected by means of an instrument known as a calorimeter, 
in which the heat produced by the complete combustion of a known 
weight of the substance under examination is absorbed by some 
calorimetric substance and its amount measured by the change of 
temperature or of physical state of the latter. The calorimetric 
substance ordinarily employed is water, the increase in tempera- 
ture of a known weight of this substance giving directly the amount 
of heat in calories. It is, of course, essential either that all the heat 
produced shall be transferred to the calorimetric substance or that 
it shall be possible to correct the observed results for any heat that 
may escape absorption. 

Another essential is that the oxidation shall be complete, a 
condition whose fulfillment it is by no means easy to secure. Two 
general methods have been employed for this purpose. The first 
was that of Thompson,* as used by Frankland and subsequently 
modified by Stohmann,| in which the oxidation is effected by 
means of pure potassium chlorate, corrections being made for the 
heat evolved in the decomposition of the latter substance. The 
second method, which has almost entirely replaced the first, con- 

* Described by Frankland, Proc. Roy. Inst, of Great Britain, June 8, 
1866, and Phil. Mag. (4), 32, 182. 

t Jour. pr. Chem., 127, 115; Landw. Jahrb., 13, 513. 



23 6 PRINCIPLES OF ANIMAL NUTRITION. 

sists in burning the substance without any admixture in highly 
compressed oxygen contained in a lined steel bomb as first devised 
by Berthelot * and subsequently modified by Mahler, Hempel, and 
Atwater. With this type of calorimeter very accurate and com- 
paratively rapid work may be done.f 

Frankland was the first to undertake determinations of the 
heats of combustion of foods and food ingredients, using the origi- 
nal form of the Thompson calorimeter. Subsequent investigators, 
of whom may be especially mentioned Stohmann, v. Rechenberg 
and Danilewski, Berthelot and his associates, Rubner, and Atwater, 
Gibson & Woods, have continued these investigations with im- 
proved apparatus and more refined methods, J and we now possess 
a considerable mass of data as to the heats of combustion of the 
more important ingredients of animals and plants and of the prod- 
ucts of metabolism. Atwater § gives the following summary of 
the results on record up to July, 1894 (see pp. 237-9). 

In the course of recent investigations into the energy relations 
of the food of man and of domestic animals a considerable amount 
of data has also been secured regarding the heats of combus- 
tion of foods and feeding-stuffs. A summary of the results of 
such determinations on 276 samples of human foods of various 
kinds has been published by Atwater & Bryant. || No similar 
compilation of heats of combustion of feeding-stuffs is as yet avail- 
able. 

It need hardly be pointed out that, taken by themselves, 
such results furnish no measure of the relative values of the 
various feeding-stuffs. Like a chemical analysis, they supply 
but a single factor, albeit an important one, for such a com- 

* Ann. dc Chirn. et de Phys., (5), 23, 160. 

t For the technical details of the method reference may be had to the 
published descriptions of the apparatus or to Wiley's Principles and Prac- 
tice of Agricultural Chemical Analysis, Vol. Ill, p. 569. 

J For a historical sketch of the development of calorimetry, as applied 
to food substances, compare Atwater, "Chemistry and Economy of Food." 
TJ. S. Department of Agriculture, Office of Experiment Stations, Bull. 21, pp 
116-126. 

§ Ibid., pp. 127 and 128. Compare also Rep. Storrs Expt. Station, 1899, 
p. 73. 

11 Rep. Conn. Storrs Expt. Station, 1899, p. 97. 



METHODS OF INVESTIGATION. 



237 



HEATS OF COMBUSTION OF ORGANIC 


SUBSTANCES 






Berthelot 
Method. 


Thompson-Stohmann Method. 




Berthe- 
lot and 

Asso- 
ciates. 


Stoh- 
rhann 
and 
Lang- 
bein. 


Stoh- 
mann 
and 
Asso- 
ciates. 


B. 

Dani- 
lewski. 


Rub- 
ner. 


Gibson. 


Albuminoids, etc. 


5990.3 






6141 
6231 


5950 

5778* 
5656* 

2523 




Elastin 


5961.3 
5941.6 

5917.8 
5907 . 8 
5885 . 1 
5867 
5849.6 
5840.9 

5745 . 1 
5735.2 

5720 5 






Plant fibrin 


5832.3 




Serum albumin 




Syntonin 






Hemoglobin 


5910 
5626 . 4 




Milk casein ■. 


5717 
5579 


5785 
5573 




u a 




Yolk of egg 


8112.4 








Vitellin 


5780 . 6 
5687.4 

5728.4 




Egg albumin 




Muscle, extractives and fat re- 
moved 




Crystallized albumin 


5672 
5662 . 6 
5640.9 
5637.1 
5553 
5510.2 
5479 
5355 1 


5598 
5324 

5511 
5362 


5709 

5069 
5493 
4909 

2537 
(3206) 




Muscle, fat removed 






u 






Blood fibrin 


5529 . 1 




Harnack's albumen 




Wool 


5564.2 




Congluten 














5298 . 8 




Fish glue 


5240 . 1 

5342 . 4 

5410.4 

5095.7 

4655 

4146.8 




Chondrin 


5130.6 
5039.9 
4979 . 6 
4650 . 3 


5637 

2465 
3053 

5642 
3428 
2621 




Ossein 




Fibroin 




Chitin 




Tunicin 




Paraglobulin 




Amids, etc. 
Urea 


2530.1 
3133.6 
4370.7 
6536 . 5 


2541.9 
3129.1 
4355.5 
6525 . 1 
4505.9 
5668.2 
2899 

3514 

3714.1 

4275.4 

2749.9 

3891.7 

5231.4 




Glvcocoll 




Alanin 

Leucin 




Sarkosin 




Hippuric acid 


5659 . 3 
2911.1 
5915.9 
3396.8 




Aspartic acid 




Tvrosin 




Asparagin 








" (water-free) 






Uric acid 


2754 




Guanin 











* Calculated ash-free. 



2 3 8 



PRINCIPLES OF ANIMAL NUTRITION. 



HEATS OF COMBUSTION OF ORGANIC SUBSTANCES (Continued). 





Berthelot 
Method. 


Thompson-Stohmann Method. 




Berthe- 
lot and 

Asso- 
ciates. 


Stoh- 
mann 
and 
Lang- 
bein. 


Stoh- 
mann 
and 
Asso- 
ciates. 


B. 

Dani- 
lewski. 


Rub- 
ner. 


Gibson. 


Fats. 
1 Animal : 

Fat of swine 




9476.9 

9485 . 7 
9493 . 6 


9380 
9357 
9406 
9410 
9330 
9345 
9324 
9398 
9192 


9686 


9423 


9515 






9427 


Fat of sheep . . . 








9530 


Fat of horse 










Fat of dog 








Fat of goose 








Fat of duck 








Fat of man 








Butter fat . 




9215.8 


9185 










10001 


2. Vegetable: 

Olive oil (expressed) 






9328 
9471 
9442 
9489 
9619 
J9130 
|9467 

3695 

3659 
3692 

3866 
3877 
3663 






9471 


it it 












Poppv-seed oil (expressed) . . 








Rape-seed " ... 








a a 








Ether extract of various seeds . 








Carbohydrates, etc. 
1. Pentoses: 

Arabinose 


3714 
3739.9 


3722 

3746 

4340.9 

4379.3 

3909.2 

3714.5 
3721.5 
3742 . 6 
3755 

3955.2 

3951.5 

3736.8 

3949.3 

3721.8 

3947 

3550 . 3 

4020.8 
3400.2 
3913.7 




Xylose 




Fucose 




(cryst.) 






2. Hex oses: 

Sorbinose 






Galactose 








3762 


3754 


Fructose 




4001 




3. Heptoses: 

Glucoheptose 


3732.8 
3961.7 




4. Disaccharids : 

Cane sugar 


3921 


Milk " 




" " (crvst.) . 


3777 . 1 


3710 


Maltose . 








" (crvst.) 






Trehalose 






" (cryst.) 






5. Trisaccharids : 

Meletriose 


4020 




" (cryst.) 











METHODS OF INVESTIGATION. 



2 39 



HEATS OF COMBUSTION OF ORGANIC 


SUBSTANCES {Continued). 


| 


Berthelot 
Method. 


Thompson-Stohmann Method. 




Berthe- 
lot and 
Asso- 
ciates. 


Stoh- 
rnann 
and 
Lang- 
bein. 


Stoh- 
mar.n 
and 
Asso- 
ciates. 


B. 

Dani- 
lewski. 


Rub- 
ner. 


Gibson. 


6. Polysaccharids: 

Glycogen 




4190.6 
4185.4 
4182.5 
4112.3 
4133.5 

4112.4 
3997 . 8 
3679.6 

9352.9 


4146 
4123 

4070 

4317 
3908 

9226 
9429 

1960 
3019 
1745 
2397 








Cellulose 


4200 
4228 
4180.4 
4187.1 

7068 






4164 


Dextran 








Inulin 




Alcohols. 

Ethyl alcohol 

Glycerin 






4001.2 
3676.8 

3490.4 


3959 


Acids. 
Palmitic 








Stearic 






Oleic 




9494.9 




Malonic 

Tartaric 


1998.2 
3006.2 




Citric 


2477.9 







parison. Just as the chemical analysis shows the total amounts 
of various substances or classes of substances present, so the heat 
of combustion shows the total amount of potential energy which 
has been stored up in the feeding-stuff. In both cases the knowl- 
edge thus acquired must be combined with data, secured in an 
entirely different way, as to the availability of these ingredients or 
this energy before we can form a judgment as to the relative values 
to the animal. 

Computation of Heats of Combustion. — The heat of com- 
bustion of a mixture of various organic substances, such as are 
contained in ordinary foods and feeding-stuffs, is equal to the sum of 
the heats of combustion of the single ingredients. If the latter are 
known we may obtain the heat of combustion of the material in 
question either by a direct calorimetric determination or by deter- 
mining chemically the proportions of the several ingredients and 
multiplying the amount of each into its known heat of combustion. 



240 PRINCIPLES OF ANIMAL NUTRITION. 

The first method, when available, is obviously to be preferred, 
and is to be regarded as indispensable in all exact investigations 
into the energy relations of the food of man or of animals. With 
materials whose proximate composition is fairly well known, how- 
ever, the agreement between the computed and the actual heat of 
combustion is very close, as has been shown by Wiley & Bigelow * 
and Slosson f for hulled cereals and cereal products. Atwater & 
Bryant, hi their publication just referred to, have discussed this 
question very fully in relation to human foods and have proposed 
a series of factors for the ingredients of the various classes of foods 
by whose use they obtain a most satisfactory agreement with the 
calorimetric results. 

On the other hand, in case of vegetable products containing 
much woody and fibrous material the actual heat of combustion 
is higher than that computed under the ordinary interpretation of 
the results of chemical analysis. Thus the actual heat of combus- 
tion of unhulled oats was found by Wiley & Bigelow to be about 
4.5 per cent, higher than the computed value, and Merrill \ has 
obtained similar results for wheat middlings and bran and for hay 
and silage. This obviously arises from the presence among the 
ill-known bodies constituting the so-called lignin and incrusting 
substances of compounds having higher heats of combustion than 
the common carbohydrates. It is not impossible that a series of 
factors similar to those of Atwater & Bryant might be worked out 
for different classes of stock foods, so that their heats of combustion 
might be computed from their chemical composition. In view, 
however, of the comparative ease and rapidity with which direct 
calorimetrie results can be accumulated it may be doubted whether 
such an undertaking would repay the labor involved. 

Methods have also been proposed and somewhat extensively 
used for computing the heat of combustion of the digested portion 
of the food. This phase of the subject, however, can be more 
profitably considered later. 

The Energy of the Excreta. — For the visible excreta (feces 
and urine) substantially the same method is available as for the food, 

* Jour. Am. Chem. Soc, 20, 304. 
t Wyoming Expt. Station, Bull. 33. 
% Maine Expt. Station, Bull. 67, p. 169. 



METHODS OF INVESTIGATION. 241 

viz., a determination of the heat of combustion. An element of 
uncertainty, however, which is ordinarily not met with in the case 
of the food, arises from the ready decomposability of the excretory 
products, which is liable to result in a loss of energy during the 
drying necessary to prepare them for combustion. The urea of 
the urine, in particular, is very readily converted into the volatile 
ammonium carbonate. Comparative determinations of nitrogen 
in the fresh and in the dried urine will show the amount of nitrogen 
lost in drying, and on the assumption that only urea is decomposed 
the loss of energy can be readily computed from the known heat of 
combustion of that substance. Atwater & Benedict * have found 
this assumption to be substantially correct for human urine, and 
the same may be presumed to be the case with the urine of carniv- 
ora. It has usually been assumed to be applicable also to the 
more complex urine of herbivora, although without, so far as the 
writer is aware, any experimental proof. 

A greater or less loss of nitrogen has also been observed in the 
drying of the feces of domestic animals, particularly of horses and 
sheep, but the nature of the material decomposed has not yet been 
investigated, and the same is true of the possible decomposition of 
non-nitrogenous materials in both urine and feces. Atwater & 
Benedict (loc. cit.) found the loss of nitrogen from human feces to 
be insignificant. 

Computation of Energy. — The computation of the energy of 
the visible excreta is much less satisfactory than in the case of the 
food on account of our inferior knowledge of the proportions and 
chemical nature of their ingredients. 

The Urine. — Formerly the urine was assumed to be substan- 
tially an aqueous solution of urea, and numerous computations of 
its energy content were made on this basis, particularly in connec- 
tion with estimates of the metabolizable energy of the proteids, 
while the same method has been applied also in estimating the 
metabolizable energy of feeding-stuffs. Rubner f was the first to 
demonstrate the serious nature of the error involved in this assump- 
tion and to show that the energy of the urine is materially greater 
than the amount thus computed. In the urine of the dog he found 

* U. S. Dept. Agr., Office of Experiment Stations, Bull. 69, p. 22. 

f Zeit. f. Biol., 20, 265; 21, 250 and 337; 42,302. Compare Chapter X. 



242 



PRINCIPLES OF ANIMAL NUTRITION. 



the energy content to be from 6.7 to 8.5 Cals. per gram of nitrogen 
in place of 5.4 Cals. as computed on the assumption that only urea 
was present, while for human urine he has obtained values ranging 
from 6.42 Cals. to 8.S7 Cals. per gram of nitrogen, and Tangl * 
has reported even higher figures. 

Kellner f has shown that the difference is still greater in the 
urine of an ox receiving only coarse fodder, the actual energy being 
about six times that computed on the above assumption and nearly 
175 per cent, of that computed after allowing for the hippuric acid 
present. In subsequent investigations J he finds that the energy 
content of the urine of cattle is much more nearly proportional to 
its carbon than to its nitrogen, being approximately 10 Cals. per 
gram of carbon. 

In six cases reported by Atwater & Benedict § in the course of 
their investigations with the respiration-calorimeter, the amount of 
energy found in human urine from a mixed diet as compared with 
that computed from the nitrogen reckoned as urea was: 







Total 
Nitrogen, 

Grms. 


Energy. 




Actual, 
Cals. 


Computed, 
Cals. 


Experiment No. 

tt it 

a a 


5 

6 

7 

8 


72.43 
64.29 
70.60 
77.90 
71.72 
77.76 


511 
504 
569 
658 
597 
589 


392 
348 
382 
421 


n tt 


9 

10 


388 
421 



Here, too, it is evident that a computation on the basis of the 
urea yields results much below the truth, and later experiments by 
the same authors have fully confirmed this result. 

The Feces. — Our knowledge of the proximate principles con- 
tained in the feces is so small that no satisfactory computation of 
their energy content is possible, except perhaps in the case of car- 
nivora on a purely meat diet, where the total amount of feces is 



* Arch. f. (Anat. u.) Physiol., 1899, p. 261. 

t Landw. Vers. Stat., 47, 275. 

% Ibid., 53, 437. 

§ U. S. Dept. Agr., Office of Experiment Stations, Bull. 63. 



METHODS OF INVESTIGATION. 243 

small. On a mixed diet containing any considerable proportion of 
vegetable matter, and particularly in the case of herbivorous ani- 
mals consuming large amounts of coarse fodders, only an actual 
determination of the heat of combustion can be depended upon. 
Since the feces of these animals contain a larger proportion of the 
indigestible lignin, etc., than does their food, the heat of combustion 
of the feces is correspondingly higher, but its actual value must 
obviously depend to a considerable degree on the character of the 
food. 

Combustible Gases. — Since it is impracticable to collect sepa- 
rately the combustible intestinal gases, we must of necessity com- 
pute the amount of potential energy carried off in these substances. 
This computation has been based on the amount of carbon con- 
tained in these gases, determined in the manner indicated on p. 72, 
upon the assumption that only methane (CH 4 ) was present. It 
has been shown that this gas exists in considerable amounts in 
the digestive tract of herbivora, and it is probable that the above 
assumption is substantially accurate, although a small amount of 
hydrogen has been found by some observers. In experiments by 
Fries,* at the Pennsylvania Experiment Station, in which both 
the carbon and hydrogen of the combustible gases excreted by a 
steer consuming chiefly timothy hay were determined, the follow- 
ing ratios of hydrogen to carbon were obtained: 

Period A. 
First day, 1:2.900 

Second day, 1:2.916 

Period B. 
First day, 1:2.978 

Second day, 1:2.947 

Period C. 
First day, 1:2.899.' 

Second day, 1:2.951 

Period D. 



First day, 1 

Second day, 1 

Average, 1 

Computed for CH 4J 1 



3.051 
3.096 



2.967 
2.976 



* Proc. Soc. Prom. Ag. Sci., 1902. 



2 44 PRINCIPLES OF ANIMAL NUTRITION. 

These results tend strongly to substantiate the belief that the 
combustible gases practically consist of methane only. 

Perspiration. — In view of the relatively minute amounts of 
organic matter contained in the perspiration it has generally been 
regarded as a negligible quantity. The data given on p. 48 for 
the nitrogen of the sensible perspiration would afford some approxi- 
mate data for computing the amount of energy contained in it. 

The Energy of Tissue Gained. — The amount of potential energy 
stored up in a gain of tissue, or the amount liberated in the kinetic 
form in case the gain is negative, cannot, of course, be made the 
subject of a direct determination. The amounts of protein and of 
fat gained or lost can, however, be determined by the methods 
described in Chapter III, and their energy content computed from 
average figures. The errors involved are those incident to the 
method of computation from the carbon and nitrogen balance, 
which have already been considered in the chapter cited, and those 
arising from uncertainty as to the exact energy content of the 
material gained by the body. 

Protein. — Just as computations of the gain or loss of protein 
by the body have been based upon the average composition of the 
proteids, so computations of its energy content have been based 
upon the average heat of combustion of these substances. The 
compilation by Atwater on pp. 237-9 contains the available data 
up to 1894. 

For approximate computations the value 5.7 Cals. per gram has 
been commonly used, while in more exact computations it has 
been assumed that the gain of protein by the animal has substan- 
tially the heat value as well as the chemical composition of fat-free 
muscular tissue (see p. 63), and the average of Stohmann's two 
determinations, viz., 5.652 Cals. per gram, has been employed. 
Kohler's investigation* of the composition of fat and ash-free 
muscular tissue (p. 64) included determinations of the heats of 
combustion which are reproduced on the opposite page. 

Fat. — Rubner, in his computations, employs the round number 
9.4 Cals. per gram for fat, while Kellner uses the value 9.5 Cals. 
Benedict & Osterberg,f whose determinations of the composition of 

* Zeit. physiol. Chem., 31, 479. 
f Amer. Jour. Physiol., 4, 69. 



METHODS OF INVESTIGATION. 



245 





No. of 
Samples. 


Heat of Combus- 
tion per Gram, 
Cals. 


Cattle 


4 
2 
2 
3 
2 
2 


5.6776 


Sheep 


5.6387 


Swine 


5.6758 


Horse 


5.5990* 


Rabbit 


5.6166 


Hen 


5.6173 







human fat are given on p. 61, found for the heat of combustion of 
the same twelve samples values ranging from 9.474 Cals. to 9.561 
Cals. per gram, the average being 9.523 Cals. Other results are 
noted in the table on pp. 237-9. 



Determination of Kinetic Energy. 

Mechanical Work. — The energy of the mechanical work done 
by the animal upon its surroundings is derived, as was seen in Part 
I, immediately from body materials and mediately from the food, 
and is one of the two forms in which kinetic energy leaves the body. 

The energy of the mechanical work done by the animal may be 
measured in various ways, the consideration of which belongs 
to the domain of mechanics and lies outside the scope of the 
present work. In general two classes of appliances have been used : 

First, dynamometers proper, in which the work is expended in 
overcoming a known resistance, produced either by friction or by 
a magnetic field, the work done being measured by the tension of a 
spring or by the amount of electric energy produced. 

Second, the tread power, in which the work, aside from that of 
locomotion, consists in lifting the body vertically and is propor- 
tional to the product of the mass of the body into the distance 
through which it is raised. 

Heat. — The second form in which kinetic energy leaves the 
body is heat. In an animal doing no work all the energy arising 
from the metabolism in the body ultimately takes this form, and 
even when mechanical work is done the larger share of the outgo 
of kinetic energy consists of heat. Part of this heat is imparted to 
the surroundings of the animal by conduction and radiation and a 

* Contained an average of 3 . 65 per cent, glycogen. 



246 PRINCIPLES OF ANIMAL NUTRITION. 

part is expended in the evaporation of water from skin and lungs 
and takes the form of the latent heat of water vapor. 

Animal Calorimeters.— The direct determination of the heat 
produced by an animal, especially a large animal, is not an easy 
task. It requires in the first place a calorimeter large enough to 
contain the animal and in the second place, for experiments of any 
length, the maintenance of a sufficient ventilating current of air 
under such conditions as shall not affect the accuracy of the calori- 
metric determination, while the latent heat of the water vapor 
carried out in the air-current must also be taken account of. In 
other words, such an apparatus must be at once a respiration appa- 
ratus and a calorimeter, and hence the name respiration-calorimeter 
has come to be applied to it. Various forms of animal calorimeters 
have been devised, some of which may be briefly mentioned. 

Lavoisier & Laplace,* in their investigations upon the origin of 
animal heat, employed an ice-calorimeter, in which the heat is 
measured by the amount of ice melted. Crawford f investigated 
the same subject using a water-calorimeter, as did, later, Dulong J 
and Despretz,§ while more recently Wood,|| and still later 
Reichert,!" have also employed the water-calorimeter. 

The ice-calorimeter, however, necessarily subjects the animal 
to an abnormally low temperature, while with the water-calorim- 
eter it has been found very difficult to secure a uniform heating of 
the different strata of water. These facts led to the employment 
of air as the calorimetric substance, the heat being measured either 
by the increase in the volume of a confined body of air at a constant 
pressure or the increase in the pressure at constant volume, and 
until quite recently the most exact methods have been based on 
this principle. 

Scharling ,** Vogel,ff and Him, JJ between 1849 and 1864, used 

* Hist. Acad. Roy. d. Sc, 1780, 355. 

t Experiments and Observations on Animal Heat. London, 1788. 

t Ann. de Chim. et de Phys. (3), 1, 440. 

%Ibid., (2), 26,337. 

|| Smithsonian Contributions, 1880. 

t Univ. Med. Mag., Phila., 2, 173. 

** Jour. pr. Chem., 48, 435. 

tt Arch. d. Ver. f. Wiss. Heilk., 1864, p. 442. 

JJ Recherches sur l'equivalent m£chanique de la chaleur. Paris, 1858. 



METHODS OF INVESTIGATION. 247 

crude forms of the air-calorimeter. In 1885 Richet * described an 
air-calorimeter for small animals, the heat being measured by the 
increase in the volume of a confined portion of air at constant press- 
ure. His experiments were of short duration (1 to 1^ hours) and 
no specific statement is made regarding ventilation and no mention 
of any determinations of the latent heat of the water vapor. 

In 1886 d'Arsonval f described a differential air-calorimeter, 
and in 1890 \ two other forms of animal calorimeter, the first being 
a water-calorimeter of constant temperature with automatic regu- 
lation of the flow of water, for which a high degree of accuracy is 
claimed, and the second an air-calorimeter, but he reports no ex- 
periments with either form. In the same year Laulanie § (see p. 70) 
described briefly a Regnault respiration apparatus which was also 
used as a calorimeter, and has subsequently reported some results 
obtained by its use. 

One of the best known forms of animal calorimeter is that of 
Rubner.|| This is essentially a Pettenkofer respiration apparatus, 
the walls of the chamber being double and the whole surrounded 
by an air space which in its turn is surrounded by a jacket con- 
taining water kept at a constant temperature. The amount of 
heat given off to the calorimeter is measured by the expansion 
under constant pressure of the confined volume of air between the 
two walls of the respiration chamber, while from comparative de- 
terminations of moisture in the ingoing and outcoming air the heat 
removed in the latent form is computed. 

Rosenthal % has constructed a somewhat similar instrument in 
which the respiratory portion is a Regnault apparatus, while the 
heat is measured by the increase in pressure of the air at constant 
volume, instead of by the increase in its volume as in Rubner's 
apparatus. Both instruments are therefore air-calorimeters, and the 
numerical values of their readings must be determined experimen- 
tally for each instrument. These two forms of apparatus are of a size 
sufficient for experiments with small animals (rabbits or small dogs). 

* Archives de Physiol , 1885, II, 237. 

t Jour, de l'Anat. et Physiol., 1886. 

X Archives de Physiol., 1890, pp. 610 and 781. 

§lbid., p. 571. 

|| Calormetrische Methodik, Marburg, 1891; Zeit. f. Biol., 30, 91. 

H Arch. f. (Anat. u.) Physiol., 1894, p. 223. 



248 PRINCIPLES OF ANIMAL NUTRITION. 

In 1894 Haldane, White & Washbournc * described a form of air- 
calorimeter in which the expansion caused by the heat produced by 
the animal in one chamber is balanced by that produced by a flame 
of hydrogen burning in a second similar chamber. The calorimeter 
is essentially one of constant volume, but the heat is computed 
from the amount of hydrogen burned. 

Laulanie f in 1895 described a Pettenkofer apparatus with small 
ventilation (see p. 71) which served also as an air-calorimeter, and 
still later J has described a differential water-calorimeter. Kauf- 
mann,§ as mentioned on p. 69, has determined the respiratory 
exchange of animals during short periods in a confined volume of 
air. The apparatus consisted simply of a zinc receptacle which 
served also as a radiation calorimeter. The internal temperature 
and that of the surrounding air were measured by recording ther- 
mometers and the loss of heat calculated according to Newton's 
law. The atmosphere in the apparatus was saturated with water- 
vapor at the start, so that the moisture excreted by the animal was 
condensed and no correction for the heat of vaporization was neces- 
sary. 

By far the most important form of respiration-calorimeter yet 
devised, however, not only as regards accuracy but particularly 
in view of the range of work of which it is capable, is that of Atwater 
& Rosa,|| tne respiratory part of which has already been mentioned 
(pp. 72 and 79). In this apparatus water is used as the calori- 
metric substance, but in the form of a constant current instead of a 
large stationary mass. As described by the authors the appara- 
tus consists of a Pettenkofer respiration apparatus provided with 
special devices for the accurate measurement, sampling, and analy- 
sis of the air-current. A current of cold water is led through copper- 
absorbing pipes near the top of 'the respiration chamber and takes 
up the heat given off by the subject. The volume of the water used 
being measured, and its temperature when entering and leaving 
being taken at frequent intervals, the amount of heat brought out 

* Jour. Physiol., 16, 123. 

t Archives de Physiol., 1895, p. 619. 

% Ibid., 1898, pp. 538 and 613. 

§ Ibid., 1896, p. 329. 

|| U. S. Dept. Agr., office of Experiment Stations, Bulletins 63 and 69. 



METHODS OF INVESTIGATION. 249 

in the water-current is readily calculated. To this is added the 
latent heat of the water-vapor brought out in the ventilating air- 
current. By means of ingenious electrical devices, a description 
of which would occupy too much space here, the temperature of the 
interior of the apparatus is kept constant, and any loss of heat by 
radiation through the walls or in the air-current is prevented. In 
test experiments the apparatus has given extremely accurate re- 
sults. 

An especial advantage of this apparatus is that it is practicable 
to make it of large size, and also to continue the experiments for an 
indefinite length of time. The original apparatus was of a size 
sufficient for experiments on man, while all previous forms were 
restricted to experiments on small animals. Recently a modified 
Atwater-Rosa apparatus has been completed under the writer's 
direction at the Pennsylvania Experiment Station, with the co- 
operation of the Bureau of Animal Industry of the United States 
Department of Agriculture, of a size sufficient for investigations 
with cattle, and still larger ones are in process of construction. 

Computation of Heat Production. — The respiration-calorim- 
eter, in its more perfected forms, is a complicated and costly appara- 
tus both in construction and use, and, moreover, is a rather recent 
development. It was natural, therefore, that attempts should be 
made to determine the heat production indirectly by computations 
based on the kind and amount of matter oxidized in the body. 

We may conveniently distinguish three distinct although closely 
related methods of attacking the problem, all of which assume as a 
fundamental postulate that the oxidation of a given substance in 
the body liberates the same amount of energy as does its oxidation 
outside the organism. In the next chapter we shall examine into 
the correctness of this postulate; for the present we are con- 
cerned simply with the methods of computation based on it. 

Computation from Gaseous Exchange. — From a knowledge of the 
ultimate composition and heat of combustion of a substance it is 
easy to compute the amount of heat which will be produced by the 
oxidation of an amount of it sufficient to yield a unit of carbon 
dioxide or to consume a unit of oxygen. Conversely, then, we can 
compute from the carbon dioxide evolved or the oxygen consumed 
in a given time the corresponding amount of energy liberated. 



25° 



PRINCIPLES OF ANIMAL NUTRITION. 



Such computations have been made by different authors for the 
three principal classes of nutrients, viz., the proteids, carbohydrates, 
and fats, the results of a few of which are as follows : 





Magnus- 
Levy.* 


Zuntz.t 


Kaufmann.t 


Laulani£.§ 




Per 

Liter 

co 2 

Cals. 


Per 

Liter 

o, 

Cals. 


Per 

Liter 

co 2 

Cals. 


Per 

Liter 

o 2 

Cals. 


Per 

Liter 

co 2 

Cals. 


Per Per 

Liter | Liter 

o„ co 2 

Cals. 1 Cals. 


Per 
Liter 

o 2 

Cals. 


Proteids || 


5.464 
6.586 
4.915 
4.976 
5.090 


4.289 
4.676 
4.915 
4.976 
5.090 


5.644 
6.628 


4.4765.569 
4 . 686 6 648 


4.647 , . 
4.650 6.571 
5.056 


4.6 


Fat 


4.6 


Dextrose 




5.056 




Starch 


5.047 


5.047 




4.95 




Cane-sugar 




" Carbohydrates" 


4.95 





















Kaufmann also computes from his theoretical equations already 
given in Part I (pp. 38 and 51) the evolution of heat per liter of 
oxygen in the various processes of partial oxidation which he be- 
lieves to take place in the body, with the following results: 

Albumen to fat and urea 4 . 646 Cals. 

" dextrose and urea . 4.460 " 

Fat (stearin) to dextrose 4.067 " 

Disregarding the minor differences in the figures of different 
authorities, it is evident that the amount of heat produced bears a 
much more constant relation to the oxygen consumed than to the 
carbon dioxide produced. For the fats and proteids, especially, the 
difference is comparatively small. In the case of an animal metab- 

* Arch. ges. Physiol., 55, 9. 

t Ibid., 68, 191. 

% Archives de Physiol., 1896, pp. 329, 342, 757. 

§ Ibid., 1898, p. 748. 

|| As pointed out on pp. 74-75 the determination of the respiratory exchange 
corresponding to a unit of proteids is not a simple matter In the table 
Kaufmann's and Laulanie's figures are based upon the theoretical equation 
(p. 75) for the conversion of albumin into carbon dioxide, water, and urea, 
while those of Magnus-Levy and Zuntz are derived largely from determina- 
tions and estimates by Rubner (Zeit. f. Biol., 21, 363) and others of the 
proximate composition of the urine of meat-fed animals. As will appear 
later, these figures are not applicable to the urine of herbivora. 



METHODS OF INVESTIGATION. 251 

olizing substantially proteids and fat, then, such as a fasting animal 
or one consuming only those two nutrients, a determination by any 
Of the methods indicated in Chapter III of the amount of oxygen 
consumed will afford the basis for at least an approximately correct 
computation of the energy liberated during the same time, par- 
ticularly when, as is often the case, the proteid metabolism consti- 
tutes but a small proportion of the total metabolism. For the 
carbohydrates the figures are somewhat higher, and where these 
bodies constitute a considerable portion of the food the error will 
be more serious, but even then the results will be of value and 
especially will afford relatively correct figures for the heat produc- 
tion on the same diet at different times. 

The computation from the gaseous exchange of the amount of 
energy liberated assumes a more exact form in case it is desired 
to determine the increment arising from some change in the 
conditions of the experiment, notably from an increase in the 
muscular work done. In the latter case, as we have seen (Chap- 
ter VI), the increased metabolism is largely or wholly that of non- 
nitrogenous matter. Such being the case, we can compute in the 
manner indicated on p. 76 from the increments of carbon dioxide 
and oxygen caused by the work the proportion of each gas corre- 
sponding respectively to the oxidation of fat and of carbohydrates, 
and from this it is easy to compute the corresponding amounts of 
energy. Thus, to take the example from Zuntz's investigations 
there given, the increments of oxygen and of carbon dioxide pro- 
duced by the performance of 1 kgm. of work in the case of a dog 
were computed to be divided as follows: 





Oxygen 

Consumed, 

c.c. 


Carbon Dioxide 

Produced, 

c.c. 


By fat 

" carbohydrates 


. 6939 
0.9765 


0.4905 
0.9765 


Total 


1.6704 


1.4670 



From this, using Zuntz's factors and assuming that there was no 
change in the proteid metabolism, the total excess of energy liber- 
ated in the body during work over that metabolized during rest is 
computed as follows: 



252 PRINCIPLES OF ANIMAL NUTRITION. 

Energy from fat 4.686 cals. X 0.6939 = 3.252 cals. 

" carbohydrates... 5. 047 cals. X 0.9765 = 4.927 '[ 



Total 8.179 " 

It is obvious that this method of computation affords the means 
of comparing the total energy metabolized during the performance 
of a measured amount of work with the quantity recovered in the 
work itself. It has been extensively used for this purpose by Zuntz 
and his associates, especially in his investigations in conjunction 
with Lehmann and Hagemann* upon work production in the horse, 
which will be considered in a subsequent chapter. The same 
authors f show that the error introduced by the assumption of 
unchanged proteid metabolism is too small to be of any significance. 
Computation from Total Excreta. — The method just described 
naturally leads up to a computation based on the gaseous exchange 
combined with a determination of the urinary products, particu- 
larly nitrogen. The latter shows the total amount of proteids 
metabolized. If we also know, or can compute with sufficient 
accuracy, the carbon, hydrogen, and oxygen of the urinary solids 
we have the data from which to compute the portion of the respira- 
tory exchange due to the protein (see p. 75) and the corresponding 
amount of energy liberated. The residues of carbon dioxide and 
oxygen can then be distributed between the fats and carbohy- 
drates in the manner already described. This method has been 
extensively employed by Kaufmann.J As already stated, he com- 
putes the gaseous exchange of the proteids on the assumption of an 
oxidation to carbon dioxide, water, and urea only, an assumption 
which, as we have seen, is in some cases considerably wide of the 
truth. 

It is, of course, essential that experiments by this method shall 
cover a sufficient length of time to ensure that the nitrogen excretion 
corresponds with the actual proteid metabolism. It is therefore 
inapplicable to periods of from a few minutes to an hour or so, such 
as have been generally employed in experiments based on the gas- 
eous exchange only. Kaufmann's experiments extended over five 

* Landw. Jahrb., 18. 1; 23, 125; 27, Supp. III. 

t Ibid., 27, Supp. III., p. 251. 

j Archives de Physiol., 1896, pp. 329, 342, 757. 



METHODS OF INVESTIGATION. 253 

hours, but it is open to serious question whether such a period is 
sufficiently long. 

Rubner * has made extensive use of a method substantially the 
same as that just outlined, but differing in details. The computa- 
tion is based upon the total nitrogen and carbon (determined or 
estimated) of urine, feces, and respiration for twenty-four (or 
twenty-two) hours, the feces' being regarded as substantially a 
metabolic product. The oxygen consumption is not determined. 
From the results for nitrogen and carbon the proteid and fat meta- 
bolism is computed in the manner explained in Chapter III (p. 78). 
For each gram of carbon in the fat metabolized Rubner reckons 
12.31 Cals. of energy, equivalent to 9.4 Cals. per gram of fat, while 
for each' gram of excretory nitrogen (urine and feces) he uses an 
energy value based on previous experiments f in which the actual 
heats of combustion of proteids and the products of their meta- 
bolism were determined. These results will be considered in another 
connection (Chapter X). The resulting values for the evolution 
of energy corresponding to each gram of excretory nitrogen are : 

Fasting (mammals) 24 . 94 Cals. 

" (birds) .......:{ 24.35 " 

Lean meat fed ... 25.98 " 

Extracted lean meat fed 26.66 " 

These factors were obtained in experiments on dogs and in 
strictness apply only to carnivorous animals. By their use, espe- 
cially if average figures are assumed for some of the minor quanti- 
ties, such as the carbon of the feces and urine, the determination 
of the heat production of a quiescent animal in this indirect way 
becomes a relatively simple matter, while comparisons with direct 
calorimetric results have shown it to be quite accurate. As was 
pointed out on p. 78, however, when carbohydrates enter largely 
into the diet the results are ambiguous, and this fact as well as 
the marked differences in the character of the excreta forbid its 
application to herbivorous animals. 

Cleavages. Hydrations, etc. — Both the above methods of comput- 
ing the heat production of an animal assume that the gaseous ex- 

* Zeit. f. Biol., 19, 313; 22, 40; 30, 73. 
t Ibid., 21, 250 and 337. 



254 PRINCIPLES OF ANIMAL NUTRITION. 

change is brought about by what is, in effect, a process of oxidation 
simply. That many other chemical processes take place in the 
body is, however, well known, and Berthelot * in particular lays 
special stress upon the possibility of numerous cleavages, syntheses, 
hydrations, and dehydrations in which the respiratory quotient 
may vary between wide limits and in which the heat production is 
not necessarily proportional to either the oxygen consumed or the 
carbon dioxide generated. An example of such a process is the 
formation of fat from carbohydrates, which, as we have seen, may 
be regarded in the light of an intra-molecular combustion in which 
no oxygen from outside is consumed, but in which there is an evolu- 
tion of heat. As an illustration of the opposite possibility — an 
evolution of heat without production of carbon dioxide — Berthelot 
instances f the oxidation of a molecule of ethyl alcohol by suc- 
cessive atoms of oxygen to ethyl aldehyde, acetic acid, glycollic 
acid, oxyglycollic acid, oxalic acid, and finally carbon dioxide and 
water. Only in the last of these stages is there an evolution of 
carbon dioxide, yet in each stage there is an evolution of heat vary- 
ing from 39.9 Cals. to 73.3 Cals. per atom of oxygen. 

But while the possibility and even probability of similar reac- 
tions in the body of the animal cannot be denied, it certainly 
seems very questionable, in the light of the results to be considered 
in the next chapter, whether they have any material bearing upon 
the determination of the general balance of energy. We know at 
least approximately the final products of metabolism, and accord- 
ing to the law of initial and final states (p. 228) the intermediate 
reactions can only affect the total amount of energy liberated in 
case some of the intermediate products are retained in the organism. 
The only material which we know to be stored up in any consider- 
able quantity in the normal body, however, is fat, and the amount 
of this we can at least approximately determine. It is of course 
possible that in an experiment covering a few minutes only, these 
intermediate reactions may seriously affect the result, but in an 
experiment covering several hours or a whole day we can hardly 
conceive such to be the case. Indeed we may probably go still 
further. It seems to be a general physiological law that the func- 
tions of the organism are adjusted to a certain average composition 
* Chaleur Animale, Part I. t Loc. cit., p. 44. 



METHODS OF INVESTIGATION. 255 

of its tissues and fluids, and that even a comparatively small varia- 
tion in the latter calls into action compensatory processes. A 
striking illustration of this is seen in the promptness with which the 
respiratory and vascular mechanism reacts to the changes produced 
in the blood by muscular activity (compare Chapter VI). It seems 
improbable, therefore, that any sufficient accumulation of the in- 
termediate products of metabolism can take place to seriously in- 
fluence the results of any but very short experiments. That the 
methods employed involve other sources of error has already ap- 
peared, but with due allowance for these it would appear that the 
results are worthy of a large degree of confidence. 

Computation from Carbon and Nitrogen Balance. — The method 
of computing the heat production from the total excreta, as em- 
ployed by Rubner and others for carnivorous animals, we have seen 
to be inapplicable to herbivora. It, however, shades naturally into 
a third method, of general applicability , which consists in combining 
with a determination of the carbon and nitrogen balance by means 
of the respiration apparatus direct determinations of the potential 
energy of the food and of the visible excreta by the methods already 
indicated. Kellner has made extensive use of this method, and the 
following example, taken from his earliest investigations,* will 
serve to show clearly the nature of the method. The ox experi- 
mented upon was fed daily 8.5 kgs of meadow hay. Respiration 
experiments showed that on this ration there was a daily gain by 
the animal of 6.2 grams of nitrogen and 127.2 grams of carbon, 
equivalent to 37.2 grams of protein and 1408 grams of fat, the 
potential energy of which can be computed from the data on p. 244. 

From determinations of the heats of combustion of food, feces, 
and urine, assuming the combustible gases excreted to consist only 
of methane, the balance of energy is computed as in the table on 
p. 256.f 

Having included under the head of outgo all the known forms 
in which potential energy as such may be disposed of, the balance 
of 14,819.5 Cals. is regarded as having been liberated as kinetic 
energy, and, since no external work was performed, to have taken 
finally the form of heat. Short of an actual calorimetric experi- 

* Landw. Vers. Stat., 47, 275. 

t The figures are the corrected ones given in Landw. Vers. Stat., 53, 9. 



256 



PRINCIPLES OF ANIMAL NUTRITION. 





Income, 
Cals. 


Outgo, 
Cals. 


Food 


32,177.3 






11,750.3 




1,945.0 




2,113.7 




211.2 


Fat " 


1,337.6 




14,819.5 








32,177.3 


32,177.3 



ment, this is the most accurate method available for determining 
the heat production of an animal during a considerable period of 
time. To short periods it is inapplicable for obvious reasons. 

Heat Production and Heat Emission. — In conclusion, it is 
important to remember that what is determined more or less accu- 
rately by all these indirect methods is the amount of energy which 
takes the kinetic form, asd in the absence of mechanical work 
finally appears as heat. In other words, what is determined is the 
heat 'production by the animal. On the other hand, the results ob- 
tained with an animal calorimeter show the amount of heat given 
off by the animal during the experiment, that is, the heat emission. 
But these two, heat production and heat emission, are by no means 
necessarily equal. On the one hand, heat produced may be tem- 
porarily stored in the body, or, on the other hand, heat retained in 
the body from a previous period may be given off along with that 
actually produced during the experiment. 

This is sufficiently obvious in case of changes in the body tem- 
perature, but eyen when the latter remains constant the possibility 
of a temporary storage of the materials of the food, and especially 
of water, in the body, must be considered. If, for example, the con- 
sumption of water in an experiment exceeds the total amount given 
off in the visible and gaseous excreta, the quantity of heat required 
to warm the excess of water to the temperature of the body remains 
in the animal as sensible heat. The heat is produced but not 
emitted. If, on the other hand, the excretion of water exceeds the 
consumption, sensible heat is removed from the body in this excess 
and the emission of heat exceeds the production by a corresponding 
amount. What is true of water is of course true also, ceteris paribus, 
of the total income and outgo of matter, although the water, on 



METHODS OF INVESTIGATION. 257 

account of its large amount and high specific heat, constitutes the 
most important factor. The skillful investigator will, of course, 
seek to plan his experiments so as to avoid these fluctuations so far 
as possible, but they can rarely be completely eliminated and 
therefore we cannot expect that the emission of heat will correspond 
exactly to the production. 



CHAPTER IX. 
THE CONSERVATION OF ENERGY IN THE ANIMAL BODY. 

Throughout the preceding chapter, particularly in considering 
the indirect methods of animal calorimetry, it has been assumed 
that the law of the conservation of energy applies to the animal 
body. This is the fundamental postulate upon which all study of 
nutrition from the standpoint of energy is based, and it is of prime 
importance, therefore, to examine into the experimental evidence 
upon which it is based. 

The processes of metabolism are essentially chemical processes, 
and, like other chemical reactions, are accompanied by thermal 
changes, resulting as a whole in a liberation of kinetic energy. 
From this point of view, then, the subject may be regarded as a 
branch of thermo-chemistry. 

The applicability of the law of the conservation of energy, and 
in particular of the law of initial and final states, to the most diverse 
chemical reactions has been amply demonstrated by the investiga- 
tions of Hess, Berthelot, Thomsen, and others. It might seem, then. 
in view of the chemical nature of metabolism, that we were justified 
in assuming the same law to apply also to the reactions taking place 
in the body, especially since investigations in other fields of science 
have led us to regard it as one of the fundamental laws of the uni- 
verse. On the other hand, however, the reactions occurring in the 
body are vast in number, are of the most varied character — oxida- 
tions, reductions, syntheses, cleavages, hydrations, etc. — are infi- 
nitely more complex than those which the chemist can produce in his 
laboratory, and finally, our knowledge of them is as yet but very 
partial and fragmentary. Moreover, the matter composing the 
body is living matter, and whatever view we may take as to the 
nature of life the properties of living matter differ from those of 

258 



THE CONSERVATION OF ENERGY IN THE ANIMAL BODY. 259 

dead matter, and we have no scientific right to assume in advance 
of the evidence that no special forces are operative in the former. 
In brief, whatever may be the probabilities in the case the applica- 
bility of the law to living beings as logically requires experimental 
demonstration as did its applicability in physics or chemistry, and 
no little labor has been within the past few years devoted to this 
problem. 

Nature of Evidence. — Before proceeding to a consideration 
of the experiments bearing upon this question it will be well to 
make clear the nature of the evidence required. 

If the law of the conservation of energy applies to the animal, 
the following are necessary consequences of it: 

1. In an animal doing no work on its surroundings and neither 
gaining nor losing body substance, the potential energy (heat of 
combustion) of the food will be equal to the potential energy of the 
excreta plus the kinetic energy given off in the form of heat plus 
the energy expended in producing physical and chemical changes in 
the body.* 

2. In an animal doing work on its surroundings, but neither 
gaining nor losing body substance, the potential energy of the food 
will be equal to the potential energy of the excreta plus the energy 
of the heat given off plus the energy of the work done plus the 
energy expended in producing physical and chemical changes in 
the body. 

3. In an animal doing no work on its surroundings, but gaining 
or losing body substance, the potential energy of the food will equal 
the potential energy of the excreta plus the energy of the heat given 
off plus the potential energy of the gain by the body (a loss by 
the body being regarded as a negative gain) plus the energy ex- 
pended in producing physical and chemical changes in the body. 

4. In an animal doing work on its surroundings and gaining or 
losing body substance the potential energy of the food will equal 
the potential energy of the excreta plus the energy of the heat given 
off plus the energy of the work done plus the potential energy of the 
gain by the body (a loss by the body being regarded as a negative 

* Such as changes of temperature or aggregation, cleavages, syntheses, 
etc. In case these resulted in an evolution of energy, this term of the equa- 
tion would, of course, have a negative sign. 



260 PRINCIPLES OF ANIMAL NUTRITION. 

gain) plus the energy expended in producing chemical and physical 
changes in the body. 

In actual experimentation it is practically impossible to so 
adjust the food that there shall be absolutely no gain or loss of body 
substance, although its amount can be made relatively small. 
Experiments on this subject, then, necessarily fall under Cases 3 
or 4, and as a matter of fact, in all the experiments hitherto 
made, the subject has either done no mechanical work or this 
work has been converted into heat inside the calorimeter and 
measured along with that directly given off by the body, so that 
all these experiments fall under Class 3. 

The quantities to be determined, then, are 

1. Potential energy of food. 

2. Potential energy of excreta (feces, urine, hydrocarbons, etc.). 

3. The heat produced (including that into which any mechani- 
cal work is converted). 

4. The potential energy of the gain or loss of body substance. 

5. The energy expended (or evolved) in producing changes in 
the body. 

If we can determine accurately these five factors, and having 
done so find the equality stated under 3 to exist in a large number 
of cases, we shall be justified in the conclusion that the law of the 
conservation of energy applies to the animal organism. 

The methods by which the first four of the above factors may be 
determined formed the subject of the preceding chapter. As re- 
gards the fifth, it has commonly been assumed that in an experi- 
ment begun and ended at the same hour of the day and under com- 
parable conditions, which has been preceded by a considerable 
period of uniform feeding and other conditions, and in which the 
subject was in apparent good health, the initial and final states of 
the body are substantially the same. While it seems highly prob- 
able that this is true, an actual demonstration of its truth is not an 
easy matter. With respect to the body temperature in particular 
it is worthy of note that even a slight variation would materially 
affect the results. Thus in a 1000-pound ox, assuming an average 
specific heat of 0.8, a variation of one fifth of a degree Celsius would 
correspond to 160 Cals. The rectal temperature affords the best 
available means of control on this point, and a very ingenious 



THE CONSERVATION OF ENERGY IN THE ANIMAL BODY. 261 

method for its determination at frequent intervals has been de- 
scribed by Benedict & Snell.* While it is true that the rectal 
temperature is not necessarily the average of that of the whole body, 
we may probably assume with safety that the variations of the two 
will substantially correspond and therefore that the error introduced 
by the use of the former will be insignificant. 

The question of possible chemical and physical changes in the 
make-up of the tissues has already been considered in the preceding 
chapter, where it was pointed out that their effect is in all proba- 
bility negligible in experiments of any considerable duration. 

Early Experiments.! — From a slightly different point of view 
the question under consideration may be stated as that of the source 
of animal heat. Is the energy given off by the animal in this form 
(in the absence of external muscular work) equivalent to the heat 
produced by the oxidation of the same materials outside the body? 
In this form the question could scarcely fail to attract attention as 
soon as man began to observe and reflect upon the phenomena of 
nature. 

The ancients regarded the "animal heat" or "vital heat" as 
" innate " and having its source in the heart. In more recent times 
it was attributed in a vague way to chemical action, and later was 
also explained as resulting from mechanical action and in particular 
from the pulsation of the blood in the blood-vessels. Our real 
knowledge of the subject, however, dates from the discovery of 
oxygen and from those researches by Lavoisier and others which 
established the true nature of combustion and laid the foundations 
of modern chemistry. 

Black I discovered that carbon dioxide was produced in animals 
by a process of combustion, and Lavoisier. § along with his more 
purely chemical researches, studied the question of animal heat and 
advanced the hypothesis that respiration consists essentially of a 
slow oxidation of the carbon and hydrogen of the food by the oxygen 
of the air, and that this slow combustion is the source of the animal 
heat. 

* Arch, ges Physiol., 90, 33. 

f This paragraph follows substantially the historical introduction to 
Rubner's paper, " Die Quelle der thierischen Warme.'' cited below. 
J Lectures on Chemistry, edited by Robison, Edinburgh, 1803 
§ Hist. Acad. Roy. d. Sci.. Paris, 1780, 355. 



262 PRINCIPLES OF ANIMAL NUTRITION. 

The first part of this hypothesis was readily susceptible of verifi- 
cation by a quantitative determination of the oxygen taken up and 
the cax-bon dioxide given off, but the second portion was too bold to 
secure general acceptance. Lavoisier, therefore, with the aid of 
Laplace, subsequently attempted to secure experimental evidence 
as to its truth. To this end they determined the amount of heat 
given off by a guinea pig in an ice-calorimeter, while in a second 
experiment the animal was placed under a bell-jar and the produc- 
tion of carbon dioxide determined. Having previously determined 
by means of the ice-calorimeter the heat of combustion of carbon, 
the results of these two trials gave them data for comparing this 
amount with that produced by the animal. The computed amount 
of heat was 25.41 Cals. ; that produced by the animal 31.82 Cals. 

Several sources of error were inherent in the experimental 
methods adopted, of some of which Lavoisier was aware, which 
tended to make the computed amount of heat too small. Taking 
these into consideration, Lavoisier considered that the experiment 
substantially confirmed his hypothesis. 

At about the same time Crawford * was investigating the same 
subject, and while his methods were rather primitive and his results 
less accurate than those of Lavoisier and Laplace, his general con- 
clusions were the same. Of later experiments may be mentioned 
especially those of Despretz f and of Dulong.J Both investigators 
employed very similar apparatus, viz., a water-calorimeter through 
which a current of air was passed, the respiratory products and the 
heat being determined in the same experiment. The proportion of 
the oxygen consumed which united with hydrogen was also deter- 
mined. Both investigators found more heat than they could ac- 
count for by the oxidation of tissue and concluded that chemical 
action is the chief but not the only source of animal heat.§ 

With the advance of physiological knowledge and the recogni- 
tion of the multiplicity and complexity of the processes taking place 
in the body, the combustion theory of the origin of animal heat 
lost rather than gained ground. A few clear-sighted physiologists 

* Experiments and Observations on Animal Heat, 1788. 

t Ann. de Chim. et de Phys. (2), 26, 337. 

% Ibid. (3), 1, 440. 

§ Compare Liebig's discussion of their experiments, Thierchemie, p. 28. 



THE CONSERVATION OF ENERGY IN THE ANIMAL BODY. 263 

still adhered to the unity and simplicity of the combustion theory ? 
but in general various subsidiary hypotheses were brought in to 
account for the observed surplus, such as the motion of the blood, 
friction, imbibition, etc. 

Rubner's Experiments. — The demonstration of the law of the 
correlation and conservation of energy in the inorganic world sup- 
plied the clue to a rational explanation of the energy manifestations 
in the living organism, while the subsequent developments of thermo- 
chemistry served also to demonstrate a material source of error in 
the older experiments on animals. In those experiments the com- 
puted heat production was based upon the amounts of carbon and 
hydrogen oxidized and the heats of combustion of those elements, 
the nitrogenous compounds not being considered. The body, how- 
ever, does not oxidize free carbon and hydrogen, but various organic 
compounds, while among its excreta are likewise incompletely 
oxidized bodies. The computed heat production, therefore, in the 
early experiments could not fail to be seriously erroneous. From 
the new point of view, therefore, there appeared no reason to seri- 
ously doubt that the animal heat has its sole source in the metab- 
olism of food and tissue, or, in other words, that the law of the con- 
servation of energy applies to the animal body. The first to under- 
take an experimental demonstration of this fact by modern methods 
was Rubner.* 

His object being primarily to investigate the source of animal 
heat, his experimental method could be somewhat abbreviated from 
the general method outlined on p. 260. No external mechanical 
work having been done by the animals, we have Case 3 of the 
four possible ones there mentioned. If we let 

F= potential energy of food, 
E= " " " excreta, 

G= " " " gain by body, 

H = hea,t produced, 

then, assuming the initial and final states of the body to be the same, 
we have 

F = E + G + H, 

* Zeit, f. Biol., 30, 73. 



264 



PRINCIPLES OF ANIMAL NUTRITION. 



which may also be given the form 

H = (F-G)-E. 

Rubner determined summarily the value of the quantity F—G 
in the second member of the last equation by the method described 
in Chapter VIII, p. 253, while the actual heat production was deter- 
mined by means of his respiration-calorimeter. 

The quantities actually determined in these experiments were 
the weight and nitrogen content of feces and urine, the carbon 
dioxide of respiration, and the heat produced. The carbon of feces 
and urine was estimated from their nitrogen and the absence of 
combustible gases in the respiratory products was assumed. From 
the total excretion of nitrogen and carbon the amounts of protein 
and fat metabolized are computed, it being assumed that all the 
excretory carbon is derived from these two substances. The corre- 
sponding amount of potential energy, equivalent to the expression 
F — G in the equation above, can readily be computed from the heats 
of combustion of fat and protein. From this the potential energy 
of the excreta must be subtracted, and this Rubner virtually com- 
putes from their total nitrogen on the basis of results obtained in 
previous experiments with similar food. 

A comparison of the heat production as thus computed with that 
actually measured by means of the calorimeter gave the following 
results : 



Food. 



Length 
of Experi- 
ment. 
Days. 



Total Heat. 



Computed, 

Cals. 



Measured, 
Cals. 



Percentage 
Difference. 



Fasting -j 

Fat 

Meat and fat ■] 

Meat -j 

Total 



5 
2 
5 

8 

12 

6 

7 



1296.3 
1091.2 
1510.1 
2492 . 4 
3985.4 
2249 . 8 
4780.8 



1305.1 
1056.6 
1495.3 
2488 . 
3958.4 
2276.9 
4769 . 3 



45 



17406.0 



17349.7 



+ 0.69 
-3.15 
-0.97 
-0.17 
-0.68 
+ 1.20 
-0.24 



-0.32 



While some of the individual experiments show not inconsider- 
able discrepancies, the averages of computed and measured heat 



THE CONSERVATION OF ENERGY IN THE ANIMAL BODY. 265 

agree very closely and, granting the entire validity of the numerous 
assumptions involved in this method, would seem to approach a 
demonstration of the applicability of the law of the conservation of 
energy to the metabolism of the animal. Aside from errors in the 
estimation of the carbon of the excreta from their nitrogen, which 
are probably small, the chief elements of uncertainty are the 
assumptions as to the nature of the material metabolized in the 
body and as to the heat of combustion of the excreta. As regards 
the former point, Rubner himself points out (Joe. cit., pp. 118-121) 
that a portion of the carbon of the respiration may be derived from 
glycogen, and even bases upon the calorimetric results in one case 
a computation of the extent to which this may have occurred. The 
latter, however, is obviously begging the question, and in his main 
computations Rubner assumes that only protein and fat were meta- 
bolized. 

Laulanie's Experiments. — By means of his differential water- 
calorimeter, Laulanie * has determined the respiratory exchange 
and the heat production of animals, both fasting and fed. The 
nitrogen excretion does not appear to have been determined. 
From the respiratory exchange the heat production is computed, 
using the data given on p. 250, and compared with that obtained 
calorimetrically. In the fasting experiments an evolution of 4.6 
Cals. of heat is computed per liter of oxygen consumed. In the 
experiments in which food was given the author computes from the 
respiratory quotient the distribution of the oxygen between fat and 
carbohydrates, neglecting the protein because it yields the same 
amount of heat per unit of oxygen as does fat, and thence calculates 
the heat production. Preliminary tests of the calorimeter, by 
allowing water to cool in it, gave respectively 101.3 per cent., 100.9 
per cent., and 99.7 per cent, of the theoretical results. The experi- 
ments show a close agreement between the observed and computed 
amounts of heat, as appears from the table at the top of page 266. 

Atwater & Benedict's Investigations. — By far the most 
extensive and complete data regarding the conservation of energy 
in the animal body are those afforded by the investigations of 
Atwater & Benedict f upon man. The experiments were made 

* Archives de Physiol ., 1898, p. 748. 

t U. S. Dept. Agr , Office of Experiment Stations, Bull. 109; Memoirs 
Nat Acad. Sci., 8, 235. 



266 



PRINCIPLES OF ANIMAL NUTRITION. 



Subject. 



Two guinea-pigs. . . 

Rabbit 

Duck 

Dog(2expts.) 

Average of all 
fasting expts.. 

Two dogs 

Guinea-pigs 

Rabbits 

Duck 

Dogs 



Food. 



Third day of fasting 

Second day of fasting . . . 

Fasting for 2 days 

" " 2 and 4 days. 



300 grms. of meat. 



! Mixed diet rich in ) 
carbohydrates "j 



Legth 
of 

Experi- 
ment, 

Hours. 



51 
4 
124 



Oxygen 
Con- 
sumed, 
Liters. 



8.112 

7.650 

8.800 

30.205 

82.812 
51.683 
31.787 
46.445 
21.603 
180.398 



Resp. 
Quo- 
tient. 



0.791 
0.752 
0.750 
0.758 

0.766 
0.816 
0.917 
0.893 
0.885 
0.973 



Heat Production. 



Ob- 

serv'd. 
Cals. 



37.106 
35.254 
40.375 
141.366 

385.403 
239.431 
155.787 
227.086 
105.911 
882.580 



Com- 
puted 
Cals. 



37.315 
35.190 
40.480 
138.943 

380.935 
237.741 
154.230 
224.050 
104.040 
887.19' 



Comp. 
+ Obs. 



100.6 
99.8 

100.3 
98.2 



99.2 
99.0 
98 6 
98.2 
100.5 



with the aid of the respiration-calorimeter of At water & Rosa (p. 
248), and in addition to the great pains bestowed to obtain accurate 
results are especially distinguished by the fact that all the quantities 
involved were, so far as possible, subjected to direct measurement, 
estimates being avoided with the necessary exception of the poten- 
tial energy of the gain or loss by the body. The sublingual or 
axillary temperature of the subject was also measured in every case. 
The following results of one of the earliest experiments (No. 5) may 
serve to illustrate the general features of them all : 





Income, 
Cals. 


Outgo, 
Cals. 




2655 
2655 






143 




128 


Loss by body : 


-24 


Fat 


-73 




2379 




102 
2655 



Aside from the loss of 97 Cals. by the body as computed from the 
carbon and nitrogen balance, all the quantities in the above state- 
ment represent actual determinations of energy and the account 
balances within 102 Cals., which is 3.8 per cent, of the total energy 
of the food or 4.1 per cent, of the computed heat production. To 
put the matter in a slightly different way, the heat production as 
computed by Kellner's method (p. 255) from the carbon and nitrogen 
balance and the energy of food and excreta exceeds by 102 Cals. 



THE CONSERVATION OF ENERGY IN THE ANIMAL BODY. 267 



the heat production actually measured by the calorimeter. This 
experiment was one of the two showing the greatest percentage 
difference between the computed and the observed heat production. 
In the following statement are tabulated the results of all the ex- 
periments thus far reported, arranged without regard to the subject 
of the experiment or the nature of the diet, but divided into two 
groups according as active muscular work was or was not performed. 





Gain 

by 

Body, 

Cals. 


Heat 
Production. 


Difference. 


Work 
Done, 

Cals. 




Com- 
puted, 
Cals. 


Ob- 
served, 
Cals. 


Cal- 
ories. 


Per 

Cent. 


Rest Experiments ; 

No. 5 


- 97 
-204 
+ 266 
+ 150 
+ 159 
+ 186 
+ 158 
+ 70 
+ 88 
+ 138 
+ 166 
+ 330 
+ 211 
-266 
+ 597 
+ 75 
+ 571 
+ 396 
+ 213 
+ 137 
+ 182 


2481 
2434 
2361 
2277 
2268 
2112 
2131 
2357 
2336 
2289 
2367 
2220 
2339 
2304 
2180 
2216 
2238 
2242 
2043 
2125 
2067 


2379 
2394 
2287 
2309 
2283 
2151 
2193 
2362 
2332 
2276 
2488 
2279 
2303 
2279 
2258 
2176 
2272 
2244 
2085 
2123 
2079 


-102 

- 40 

- 74 
+ 32 
+ 15 
+ 39 
+ 62 
+ 5 

- 4 

- 13 
+ 121 
+ 59 

- 36 

- 25 
+ 78 

- 40 
+ 34 
+ 2 
+ 42 

- 2 
+ 12 


-4.1 
-1.6 
-3.2 

+ 1.4 
+ 0.7 
+ 1.8 
+ 2.9 
+ 0.2 
-0.2 
-0.6 
+ 5.1 
+ 2.7 
-1.5 
-1.1 
+ 3.6 
-1.8 
+ 1.5 
+ 0.1 
+ 2.0 
-0.1 
+ 0.6 




" 7 




" 8 




" 9 




" 10 




" 13 




" 14 




" 15 




" 16 




" 17 




" 18 




" 19 




" 20 




" 21 




" 22 




" 23 




" 24 




" 25 




" 26 




" 27 




" 28 








Totals 


+ 3525 

-415 
-391 
-308 
-255 
-234 
-164 
-347 
-451 
-388 


47387 

3829 
3901 
3922 
3515 
3479 
3439 
3573 
3669 
3629 


47552 

3726 
3932 
3927 
3589 
3470 
3420 
3565 
3632 
3487 


+ 165 

-103 
+ 31 
+ 5 
+ 74 

- 9 

- 19 

- 8 

- 37 
-142 


+ 0.35 

-2.7 
+ 0.8 
+ 0.1 
+ 2.1 
-0.3 
-0.6 
-0.2 
-1.0 
-1.2 




Work Experiments : 

No. 6 


250 

186 
200 
255 
249 
249 
196 
197 
250 


" 11 


" 12 


" 29 


" 30 


" 31 


" 32 


" 33 


" 34 




Totals 


-2953 

+ 572 


32956 
80343 


32748 
80300 


-208 
- 43 






Totals, rest and work 


n n^ 









268 PRINCIPLES OF ANIMAL NUTRITION. 

In the former case the observed heat production includes the heat 
into which the work was converted. 

The total of all the experiments shows an almost absolute agree- 
ment between the computed and the observed results. To a trifling 
extent, however, this arises from a compensation between the rest 
and work experiments, the computed heat tending to be slightly 
too small in the former and slightly too great in the latter, but the 
agreement in each series is so close as to amount to a demonstra- 
tion of the applicability of the law of the conservation of energy to 
the metabolism of the animal organism. 



CHAPTER X. 

THE FOOD AS A SOURCE OF ENERGY— METABOLIZABLE 

ENERGY. 

With the establishment of the law of the conservation of 
energy in its application to the animal body, and with the 
development of the methods of calorimetric research briefly out- 
lined in Chapter VIII, it has become possible to study success- 
fully the problems of animal nutrition from a new standpoint, re- 
garding the food as primarily a source of energy to the body and 
tracing, to some extent at least, the transformations which that 
energy undergoes in the organism and particularly the extent to 
which the latter utilizes it for various purposes. 

Some data regarding the total energy of foods and their constitu- 
ents have already been given in Chapter VIII. It was there pointed 
out, however, that the total energy, taken by itself, does not fur- 
nish a measure of the nutritive value of a substance. It is now 
necessary to enter upon the question of the availability of this 
energy to the organism. 

Total and Metabolizable Energy. — The heat of combustion 
of the food represents to us its total store of potential energy. By 
no means all of this potential energy, however, is accessible to the 
organism. A part of what the animal eats is not food at all in a 
physiological sense, but is simply waste matter which passes through 
the digestive tract unacted upon. Furthermore, that part of it 
which is digested and resorbed is not completely oxidized in the 
body, but gives rise to the formation of excretory products which are 
still capable of liberating energy by oxidation. We have, there- 
fore, at the outset, to distinguish between the total or gross, 
energy of the food eaten, represented by its heat of combustion, 
and the portion of that energy which can be liberated and utilized in 

269 



270 PRINCIPLES OF ANIMAL NUTRITION. 

the organism. It is only this latter portion, of course, of which the 
body can avail itself, and the term available energy has, therefore, 
very naturally been proposed for it. 

As will appear later, however, the terms available and availa- 
bility may also be employed, and have actually been used, in a more 
restricted sense to designate that part of the energy of the food 
which can be applied directly by the organism to purposes other 
than simple heat production. In order to avoid the confusion of 
terms thus arising it has been proposed to modify the term available 
by the words gross and net. The gross available energy, according 
to this terminology, signifies all of the total energy of the food 
which can be utilized by the body for any purpose whatever; 
that is, it is available energy in the first of the two senses defined 
above. Similarly, the net available energy signifies the available 
energy in the second sense, or energy available for other purposes 
than simple heat production. The term " fuel value " has also been 
employed by some writers, notably by Atwater, to designate the 
gross available energy. 

It appears to the writer desirable, however, to avoid the double 
use of the word available, even with the somewhat awkward modi- 
fying terms proposed. Strictly speaking, what is meant by gross 
available energy in the above sense is that portion of the potential 
energy of the food which the digestive and metabolic processes of 
the organism can convert into the kinetic form, and its measure, 
according to the principles enunciated in Chapter VII, is the differ- 
ence between the potential energy of the food and the potential 
energy of the various forms of unoxidized matter rejected by the 
organism. In other words, it is that fraction of the energy of the 
food which can enter into the metabolism of energy in the body. 
The writer, therefore, tentatively proposes for it the term metabo- 
lizable energy, as expressing the facts without any implication as to 
the uses made by the body of the energy thus metabolized. 

Metabolizable energy, then, may be briefly defined as potential 
energy of food minus potential energy of excreta, including under 
excreta, of course, all the wastes of the body, visible and invisible. 
The method is analogous to that of the determination of digestibility. 
In both cases it is a calculation by difference, and the result shows 
simply the maximum amount of matter or of energy put at the dis- 



THE FOOD AS A SOURCE OF ENERGY. 271 

posal of the organism without affording any clue to the use made 
of it by the latter, that is, to its availability in the more restricted 
sense. 

In actual investigation, of course, the metabolizable energy of 
the food is most accurately found by means of direct determinations 
of the heats of combustion of the food and the waste products. 
Except in the case of the intestinal gases no serious difficulties 
stand in the way of these determinations, and with the present im- 
proved and simplified methods of calorimetry it may fairly be 
expected that, in exact experiments, at least the energy of the food, 
feces, and urine will be directly determined, while it is not impossi- 
ble that more extended investigations than are now available may 
enable us to make, for different classes of materials, a fairly accurate 
estimate of the intestinal gases. As results accumulate from such 
investigations we shall gradually acquire a fund of information 
regarding the amount of metabolizable energy contained in foods 
and feeding-stuffs which it is perhaps not chimerical to suppose may 
one day largely take the place of our present tables of composition 
and digestibility. 

Up to the present time, however, but a comparatively small 
number of experiments upon domestic animals are on record in which 
the metabolizable energy of the food has been actually determined. 
In a somewhat larger number of cases the loss of energy in feces 
and urine has been determined, and in others that in the feces only. 
As regards human food the data are somewhat more abundant, 
but nevertheless by far the greater part of our scientific knowledge 
of foods and feeding-stuffs is expressed in terms of (conventional) 
chemical composition and apparent digestibility. If, therefore, we 
would not forego the advantages which may be anticipated from a 
study, from the new point of view, of the accumulated results of 
the last half-century of experimental work in this domain, it is im- 
portant that we be able to estimate as accurately as may be the 
metabolizable energy of the food from its known or estimated com- 
position and digestibility. Not a little labor has been expended 
upon both aspects of the subject, particularly by Rubner in relation 
to the carnivora and man, by Atwater and his associates with rela- 
tion to human nutrition, by Kellncr as regards ruminants, and by 
Zuntz and his associates in the case of the horse. 



272 PRINCIPLES OF ANIMAL NUTRITION. 

§ i. Experiments on Carnivora. 

The comparative simplicity and completeness of the digestive 
processes of carnivora, together with the great variations which can 
be made in their diet, have made them favorite subjects for physio- 
logical experiments. It is possible to feed a dog or cat on what are 
close approximations to simple nutrients for a sufficient length of 
time to permit an accurate determination of the waste products, 
while with herbivora this is impracticable for obvious reasons. 

While earlier experimenters, among whom may be mentioned 
Frankland,* Traube.f and Zuntz,J have concerned themselves with 
the question of the energy values of foods and nutrients, it is to the 
fundamental researches of Rubner that we owe not merely more 
accurate determinations of metabolizable energy, but in particular 
a clearer conception of its actual significance in nutrition. Rubner's 
experiments § were made chiefly with dogs and were directed 
toward the determination of what he designates as the physiological 
heat value of the more important proteid foods, corresponding 
substantially to what is here called the metabolizable energy. 

Proteids. — As regards the non-nitrogenous ingredients of the 
food, Rubner assumes that, so far as they are digested, their metab- 
olizable energy is the same as their gross energy, or, in other words, 
that there are no waste products. For example, if a dog is given a 
certain amount of starch and none appears in the feces it is assumed 
that the starch has simply undergone hydration and solution in the 
digestive tract without material loss of energy and that conse- 
quently the full amount of energy contained in the starch is avail- 
able in the resorbed sugar for the metabolism of the body. In 
herbivora we know that there is a considerable production of gas- 
eous hydrocarbons by fermentation in the digestive tract. The 
respiration experiments of Pettenkofer & Voit on dogs, however 
(compare p. 72), showed but a small excretion of such gases, while 
Tappeiner || denies the presence of methane in any part of the dog's 
alimentary canal. In the case of carnivora, then, the above 

* Phil. Mag. (4), 32, 182. 

t Virchow's Archiv., 29, 414. 

j Landw. Jahrb.. 8, 65. 

§ Zeit. f. Biol., 21, 250 and 337. 

|| Quoted by Rubner, ibid., 19, 318. 



THE FOOD AS A SOURCE OF ENERGY. 273 

assumption is at least in harmony with current opinion. Rubner's 
■experiments were therefore directed to the determination of the 
metabolizable energy of the proteids. 

The earlier computations of the metabolizable energy of the 
proteids by Frankland, Traube, Danilewski, and others * were af- 
fected by two sources of error. First, the heats of combustion as 
determined by the imperfect calorimetric methods then available 
were seriously in error. Second, the manner of computing the 
metabolizable energy from these data has been shown by Rubner 
to be incorrect. Previous to his investigations the metabolizable 
energy of the proteids had been very generally computed by deduct- 
ing from their gross energy the energy of the corresponding amount 
of urea. In other words, it was assumed that all the nitrogen of the 
proteids was split off in the form of urea and excreted in the urine, 
which was accordingly regarded as being practically an aqueous 
solution of urea, and that the non-nitrogenous residue of the proteids 
was completely oxidized to carbon dioxide and water. Rubner's 
results show that this assumption is seriously erroneous and gives 
too high results for the metabolizable energy. 

In the first place, it neglects entirely one of the waste products, 
viz., the feces. The latter are to be regarded in the carnivora, 
especially on a proteid diet, as a true excretory product, comparable 
to the organic matter of the urine and containing at most but traces 
of undigested food. This was early pointed out by Bischoff & 
Voit f and is now generally admitted by physiologists. (Compare 
p. 47.) In Rubner's experiments somewhat over 3 per cent, of 
the energy of the proteid food was found in the feces. 

In the second place. Rubner shows that the urine is far from 
being a simple solution of urea. J His previous investigations § had 
shown that the extractives of lean meat, the form of proteid most 
commonly used in such experiments, pass through the system un- 
changed and are excreted in the urine, thus increasing its content of 
energy. By feeding meat previously treated with water to remove 

* Cf. Rubner, loc. tit., p. 341. 

t Ernahrung des Fleischfressers, p. 291; compare also Muller, Zeit. f. 
Biol., 20, 327; Rieder, ibid., 20, 378; Tsuboi, ibid., 35, 68. 
% Compare Chapter VIII, p. 241. 
§ Zeit. f. Biol., 20, 265. 



274 PRINCIPLES OF ANIMAL NUTRITION. 

these extractives, he demonstrates that in this case also the urine 
is far from being a simple solution of urea. With a daily excretion 
of 13.22 grams of total urinary nitrogen, there was found in the urine 
0.105 gram of kreatinin, 0.656 gram of cyanuric acid, and an un- 
determined amount of phenol. The proportion of carbon to nitro- 
gen in the urine was also notably higher than in urea, viz., 0.523 : 1 
in place of 0.428: 1, or an excess of about 20 per cent. Rubner 
concludes that the only sure method of ascertaining the amount of 
potential energy carried off in the urine is the direct determination 
of its heat of combustion. Accordingly, in the experiments under 
consideration, the urine was dried on pumice-stone and burned in 
the calorimeter, a correction being made for the urea decomposed 
during the drying. Danilewski,* about the same time, also re- 
ported determinations of the heat of combustion of the dry matter 
of human urine which, like Rubner's, show an excess over that 
computed from the urea present. 

The materials experimented on by Rubner were prepared lean 
meat, such as has been commonly used in feeding experiments r 
and meat with the extractives removed by treatment with water, 
the gross energy of each being determined by burning the dried 
material in the calorimeter after having removed the fat by extrac- 
tion with alcohol and ether.f The prepared material (in the moist 
state) was fed to dogs for from five to eight days, during all or a 
portion of which time the feces and urine were collected and their 
content of nitrogen and energy determined. The amounts fed are 
not stated, but the percentage of the total nitrogen fed which 
reappeared in the feces is given. A third experiment on a fasting 
dog was added in which the urine of the second, third, and fourth 
days was collected and examined. 

So far as the proteids are metabolized in the body all their nitro- 
gen which does not reappear in the feces will be found in the urine. 
On this basis the nitrogen per gram of dry proteids metabolized in 
these experiments was divided as shown in the following table. In 
the case of the fasting animal, Rubner believes himself justified, on the 
basis of other experiments, in assuming that the nitrogenous tissue 

* Arch. ges. Physiol., 36, 230. 

t Subsequent investigations have shown that the material thus prepared 
still contains traces of fat. 



THE FOOD AS A SOURCE OF ENERGY. 



2 75 



metabolized had substantially the same composition and heat-value 
as the lean meat of the first experiment, and the feces are also 
assumed to be similar. 



Food. 


Nitrogen of 
Food, 
Grms. 


Nitrogen of 
Feces, 
Grms. 


Nitrogen of 
Urine, 
Grms. 


Lean meat 


0.1540 
0.1659 
0.1659 


0.0024 
0.0023 
0.0023 


0.1516 
0.1636 
0.1636 


Extracted lean meat 

Nothing (bodv tissue) 



The energy of the excretory products, calculated per gram of 
nitrogen, was as follows : 



Food. 


Urine, 
Cals. 


Feces, 
Cals. 


Lean meat 

Extracted lean meat 

Nothing 


7.450 
6.695 
8.495 


70.290 
81.515 



A comparison of the above results for the urine with the energy 
of urea (5.41 Cals. per gram of nitrogen) fully confirms the conclu- 
sions already drawn from its chemical composition. 

From the figures of the last two tables, together with the heats 
of combustion found for the food consumed, viz., 

Lean meat, fat removed 5 . 345 Gals, per gram 

" " extractives and fat removed... 5. 754 " " " 

we can readily compute the energy of the excreta and by difference 
the metabolizable energy of the food per gram, as follows: 





Lean Meat. 


Extracted 
Lean Meat. 


Nitrogenous 
Body Tissue. 


Energy of food 


Cals. 


Cals. 
5.3450 


Cals. 

0.1854 
1 . 0945 
4.4741 


Cals. 
5 . 7540 


Cals. 

0.1683 

1.2878 
3 . 8889 


Cals. 
5 3450 


" '' feces 

" " urine 


0.1683 
1 . 1294 




Metabolizable energy 










5.3450 


5.3450 


5.7540 


5.7540 


5.3450 


5.3450' 



276 



PRINCIPLES OF ANIMAL NUTRITION. 



Rubner makes a slight correction in the above figures for the 
energy of hydration and solution. The energy of the proteids was 
determined in the dry state. They were fed, however, moist, and 
it is known that an evolution of heat takes place when dry proteids 
are brought in contact with water. Consequently the potential 
energy of the moist proteids is less than that computed from the 
calorimetric results. Rubner estimates this loss (loc. cit., p. 307) at 
0.5 per cent. The urea leaves the body in solution. Its solution 
in water, however, causes an absorption of heat equal to 2.4 per 
cent, of the total energy of the urea, and accordingly (neglecting 
other organic matter) the heat value of the urine is higher than that 
calculated from the calorimetric results upon the dried urine. Both 
these errors tend to make the metabolizable energy appear too 
great. Rubner' s corrections are as follows: 



Lean Meat. 
Cals. 



Extracted 

Lean Meat. 

Cals. 



Nitrogenous 

Body Tissue, 

Cals. 



Metabolizable energy as above 

Energy of hydration 

" " solution 

Corrected metabolizable energy 



4.0473 
0.0269 
0.0199 
4.0005 



4.4741 
0.0288 
0.0215 
4.4238 



3 . 8889 
0.0269 
0.0199 
3.8421 



The energy lost in hydration is. of course, practically a diminu- 
tion of the gross energy of the food. The energy absorbed in the 
solution of the urea can be regarded either as a part of the energy of 
the excreta or as being a part of the general expenditure of energy 
by the body in internal work. (See the next chapter.) 

Rubner * has also computed the metabolizable energy of a num- 
ber of proteids for which direct determinations are wanting. For 
this purpose he uses the results of Stohmann f for the gross energy 
and assumes, first, that the nitrogen will be divided between feces 
and urine in the same ratio as in the experiment on extracted lean 
meat, and second, that the energy of these excretory products per 
gram of nitrogen will be the same as in that experiment. He thus 
obtains the following results: 

* Loc. cit., p. 351. 

t Landw. Jahrb., 13, 513. 



THE FOOD AS A SOURCE OF ENERGY. 



277 



Substance. 



Per Cent. 

Nitrogen. 


Gross 

Energy 

Per Grm., 

Cals. 


Loss in 

Excreta, 

etc., 

Cals. 


15.6 


5.634 


1.263 


15.7 


5.577 


1.270 


15.2 


5.715 


1.311 


16.6 


5.754 


1.329 


16.6 


5.508 


1.329 


15.4 


5.345 


1.345 


17.5 


5.359 


1.390 


19.2 


5.595 


1.555 


15.4 


5.345 


1.503 



Metaboliz- 

able Energy 

Per Grm., 

Cals. 



Paraglobulin 

Egg albumin 

Casein 

Syntonin 

Fibrin 

Lean meat 

Conglutin 

Crystallized albumin . . . 
Nitrogenous body tissue 



4.371 
4.307 
4.404 
4.424 
4.179 
4.000 
3.969 
4.090 
3.842 



§ 2. Experiments on Man. 

Protein. — Rubner * has also reported a single experiment on a 
man upon a diet of meat with a slight addition of fat. The results, 
expressed in the same manner as those given in the preceding sec- 
tion, that is, per gram of dry matter of the meat, were — 

Energy of food 5.599 Cals. 

" feces 0.434 Cals. 

" urine 1.027 " 

Metabolizable energy 4. 138 " 

5.599 " 5.599 " 



Quite a number of determinations are on record of the ratio be- 
tween the nitrogen and the energy content of human urine. Rub- 
ner t reports the following results upon various diets, including the 
experiment on meat just quoted: 

Diet. Energy Per Grm., 

JN ltrogen. 

Mother's milk 12. 10 Cals. 

Cow's milk— infant..... 6.93 " 

" —adult 7.71 " 

Mixed diet, poor in fat 8.57 " 

it it tt it a q 00 it 

" " richinfat 8.87 " 

ti It It it It o ^ ft 

" " " "—boy.'..'.'.'.'.'.'.'.'.'.'.'.'.'.'.' 6.42 " 

Mixed diet — boy 7 . 50 " 

Meat 7.69 " 

Potatoes 7.85 " 

* Zeit f. Biol., 42, 272. f Hid-, P- 302. 



278 PRINCIPLES OF ANIMAL NUTRITION. 

With the exception of the mother's milk, the results show but a 
slightly greater range than those on the dog. The results of Atwater 
& Benedict * cited on p. 242, when computed per gram of nitrogen, 
give the following results: 

Experiment No. 5 7.055 Cals. 

" 6 7.839 " 

« « 7 8.060 " 

" « 8 8.447 " 

« " 9 8.326 " 

« "10 .7.575 " 

The same authors report f the average of 46 determinations as 
7.9 Cals. per gram of nitrogen. Tangl % has reported materially 
higher figures, especially for diets containing large amounts of 
carbohydrates and fat. 

In the case of a mixed diet more or less of the potential energy 
of the feces may be derived from the non-nitrogenous nutrients 
of the food, and we should hardly be justified in making for these 
experiments a computation like that made for the meat diet. The 
rather small range of the figures in most cases, however, would 
seem to show that the metabolizable energy of the proteids of ordi- 
nary mixed dietaries is substantially the same as that found by 
Rubner for carnivora. Tangl' s results perhaps suggest the possi- 
bility of the occasional presence in human urine of non-nitrogenous 
matters similar to those found so abundantly in that of ruminants. 
Rubner's Computations. — Rubner's earlier researches did not 
include experiments upon man, but from the results given in the 
foregoing section he endeavored to compute approximate factors 
for the metabolizable energy of the mixed diet of man.§ For this 
purpose he estimates that, on the average, 60 per cent, of the pro- 
tein of the diet is derived from animal sources and 40 per cent, from 
vegetable. For the animal protein he uses the value found above 
for lean meat, and for vegetable protein the average of the values 
for syntonin and fibrin (since these have an ultimate composition 

* U. S. Dept. Agr., Office of Experiment Stations, Bull. 69. 
t Report Storrs Expt. Station, 1899, p. 100. 
% Arch. f. (Anat. u.) Physiol., 1899, 261. 
§ Loc. tit., p. 370. 



THE FOOD AS A SOURCE OF ENERGY. 2/9 

similar to that of the proteids of the grains). Correcting these 
values for the error involved in the usual computation of protein 
from nitrogen, he obtains as the average metabolizable energy of 
the protein (N X 6.25) of a mixed diet 4.1 Cals. per gram. 

For the fat and carbohydrates it is assumed that all their poten- 
tial energy is metabolizable, but an allowance is made in the latter 
case for the error due to the ordinary computation of the carbo- 
hydrates by difference and for some minor sources of uncertainty. 
Rubner's final averages are — 

Protein (NX6.25) 4.1 Cals. per gram. 

Fat 9.3 " " 

Carbohydrates 4.1 " " 

The value for protein, by the method of computation, includes 
an allowance for the metabolic products contained in the feces, but 
neither it nor the values for the other nutrients include any estimate 
for the loss through imperfect digestion. In other words, they 
refer to the digested nutrients. 

These figures were designed expressly for computing the metab- 
olizable energy of human dietaries, and even for that purpose are 
confessedly only approximations. In the absence of more exac 
figures, however, they have been somewhat extensively used for 
computing the metabolizable energy of the digested portion of the 
food of domestic animals. For purposes of approximate estimates 
such a use of them was perhaps justifiable, but in too many cases 
their origin seems to have been forgotten and a degree of accuracy 
ascribed to them which they do not possess. As will be shown 
presently, later investigations have yielded materially different 
results for the metabolizable energy of the several classes of nutri- 
ents in the food of herbivorous animals. 

Later Experiments. — Quite recently Rubner * has published the 
results of some experimental investigations into the validity of the 
averages or "standard figures " given above. In these experiments 
the weights and heats of combustion of food, feces, and urine were 
determined calorimetrically and the metabolizable energy as ob- 
tained from these data was compared with that computed by the use 
of the above factors. In making the latter calculation an allowance 

*Zeit. f. Biol., 42, 261. 



280 



PRINCIPLES OF ANIMAL NUTRITION. 



was made for the percentage loss in the feces equal to that observed 
in the actual experiment. The results for the metabolizable energy 
per day were — 



Diet. 


From 

Calorimetric 

Data, 

Cals. 


Computed, 
Cals. 


Potatoes only 


1911.4 
2060.4 
1773.1 
2400.5 
2698.8 
2574 . 1 
2549 . 6 
1746.8 
1765.5 


1911.5 


Rve bread, bolted flour 


2079.3 


" " unbolted flour 


1758.6 


Mixed diet, poor in fat 

" " rich " " 


2376.0 
2600.0 


" " and carbohyd's -j Jj 


2608.0 
2610.0 
1724.3 
1737.3 



As above noted, the computed results include a deduction for 
the energy of the undigested matter in the feces. Rubner finds that 
the heat of combustion of the organic matter of the latter varies 
but little even on extremes of diet, so that the loss through this 
channel is approximately proportional to the amount of the ex- 
cretion. In the experiments on mixed diet the percentage loss of 
energy in the feces varied from 4.3 per cent, to 7.9 per cent, of 
the energy of the food. 

Atwater's Investigations. — By far the most extensive data 
as to the metabolizable energy of human foods and dietaries are 
those derived from the investigations upon human nutrition made 
under Atwater's direction by the United States Department of 
Agriculture with the cooperation of Wesleyan University, the 
Storrs Experiment Station, and various other experiment sta- 
tions. Atwater & Bryant* have summarized these results in a 
preliminary report of which the essential features are given in 
the following paragraphs. 

From the best data available, the heats of combustion of the 
protein, carbohydrates, and fats of various classes of foods are esti- 
mated. In these estimates account is taken as fully as possible of 
the proportion of nitrogen in proteid and non-proteid forms, and 
of the varying percentage of nitrogen in different proteids, the nitro- 
gen factors used being those quoted on p. 6. The accuracy of 

* Report Storrs Agr. Expt Station, 1899, p. 73. 



THE FOOD AS A SOURCE OF ENERGY. 281 

these estimates is checked by a comparison of the computed with 
the actual heats of combustion of 276 different samples of food, the 
average results showing a close agreement. Assuming the potential 
energy of the urine to be all derived from the proteids, the average 
of 7.9 Cals. per gram nitrogen given above (p. 278) corresponds to 
1.25 Cals. per gram of protein (NX6.25) metabolized. The loss of 
energy in the feces is estimated from a number of digestion experi- 
ments upon single foods, the results being checked by a comparison 
of the actual and computed apparent digestibility in 93 digestion 
experiments on mixed diet. Finally, the proportions of the several 
nutrients which are derived from different classes of foods in 
average mixed diets are computed from the results of 185 dietary 
studies. The final results thus obtained for the metabolizable 
energy or " fuel value " of the nutrients are shown in the table on 
page 282. 

The average results for the ordinary mixed diet of man were — 

Protein 4.0 Cals. per gram 

Carbohydrates 4.0 " " " 

Fat 8.9 " " 

These factors are smaller than those proposed by Rubner, largely 
because they relate to the total and not to the digested nutrients. 
Comparisons of the computed with actual metabolizable energy of 
mixed dietaries, using the factors of the above table, gave concor- 
dant results. 

§ 3. Experiments on Herbivora. 

The Mockern Investigations. — The larger share of our present 
knowledge regarding the metabolizable energy of the food of her- 
bivora is due to the investigations upon mature cattle which have 
been made by Kellner * since 1894 at the Mockern Experiment 
Station. In the earlier series of experiments (including those by 
G. Kuhn, reported by Kellner f) additions of commercial wheat 
gluten and of starch were made to a basal ration consisting exclu- 
sively of coarse fodder (hay or straw). In the later series of ex- 
periments additions of the same substances and of oil and beet 
molasses on the one hand, and of coarse fodders on the other hand, 
were made to a mixed basal ration. 

* Landw. Vers. Stat., 47, 275; 50, 245; 53, 1. f Ibid., 44, 257. 



PRINCIPLES OF ANIMAL NUTRITION. 





Nutrients 
Furnished 
by Each 
Group per 
100 Grms. 
Total. 


Heats of 
Combus- 
tion per 
Grm. 


Propor- 
tion of 
Total 
Nutrients 
Actually 
Avail- 
able. 


Total 
Energy 
per Grm. 
in Avail- 
able Nu- 
trients. 


Fuel Value. 


Kind of Food 
Material. 


Per Grm. 
Available 
Nutrients. 


Per Grm, 
Total 
Nutri- 
ents. 


Protein: 

Meats, fish, etc . . . 

Eggs 

Dairy products . . . 


Grms. 

43.0 

6.0 

12.0 


Cals. 
5.65 
5.75 
5.65 


Per Cent. 
97 
97 
97 


Cals. 

5.50 
5.60 
5.50 


Cals. 

4.40 
4.50 
4.40 


Cals. 
4.25 
4.35 
4.25 


Animal food .... 

Cereals 

Legumes 

Vegetables 

Fruits 


61.0 

31.0 
2.0 
5.5 
0.5 


5.65 

5.80 
5.70 
5.00 
5.20 


97 5.50 

85 4 . 95 
78 4.45 
83 4.15 
85 4.40 


4.40 

4.55 
4.45 
3.75 
3.95 


4.25 

3.70 
3.20 
2.90 
3.15 


Vegetable food . 
Total food 

Fat: 

Meat and eggs .... 
Dairy products . . . 


39.0 
100.0 

60.0 
32.0 


5.65 
5.65 

9.50 
9.25 


85 
92 

95 

95 


4.80 
5.20 

9.00 

8.80 


4.40 
4.40 

9.50 
9.25 


3.55 
4.00 

9.00 

8.80 


Animal food .... 
Vegetable food . 


92.0 
8.0 


9.40 
9.30 


95 
90 


8.95 
8.35 


9.40 
9.30 


8.95 
8.35 


Total food 

Carbohydrates : 

Animal food .... 
Cereals 


100.0 

5.0 
55.0 

1.0 
13.0 

5.0 
21.0 


9.40 

3.90 
4.20 
4.20 
4.20 
4.00 
3.95 


95 

98 
9S 
97 
95 
90 
98 


8.90 

3.80 
4.10 
4.05 
4.00 
3.60 
3.85 


9.40 

3.90 
4.20 
4.20 
4.20 
4.00 
3.95 


8.90 

3.80 
4.10 


Legumes 

Vegetables 

Fruits 


4.05 
4.00 
3.60 


Sugars 


3.85 


Vegetable food . 
Total food 


95.0 
100.0 


4.15 
4.15 


97 
97 


4.00 
4.00 


4.15 
4.15 


4.00 
4.00 



In each experiment the digestibility of the ration was deter- 
mined in the usual manner, and also the carbon of food, feces, urine, 
and respiration (including methane, etc.), and the nitrogen and 
heats of combustion of food, feces, and urine. The experiments 
were made with every precaution and extended over a sufficient 
length of time to ensure normal results. In each experiment the 
respiratory products were determined in four or five separate periods 
of twenty-four hours each. No such complete experiments with 



THE FOOD AS A SOURCE OF ENERGY. 283 

other classes of herbivorous animals have been reported, although 
partial data are available from experiments on horses and swine. 

Method of Stating Results. — The determination of the 
metabolizable energy of a given ration by experiments like 1 the 
above is, in principle, very simple, although requiring many appli- 
ances and much technical skill. When, however, we attempt to 
generalize the results much greater difficulties are encountered 
than in the cases previously considered. 

In investigations upon carnivora and upon man the metaboliz- 
able energy, as we have just seen, is usually computed upon the 
total nutrients of the food — that is, upon the total amounts of 
protein, carbohydrates, and fat — the deduction for the loss of 
energy in the feces being included in the factors employed. This 
is possible because the amount of potential energy thus removed 
is small in itself and subject to relatively small variations on ordi- 
nary diet and also because the crude nutrients composing the food 
are largely chemical compounds which are at least fairly well 
known. 

The food of herbivora, on the contrary, is both more complex 
and less well known chemically and contains a much larger and Very 
varying proportion of indigestible matter. As a consequence the 
feces, instead of being chiefly an excretory product, consist mainly 
of undigested food residues with but a small proportion of meta- 
bolic products, and contain a large and variable part of the total 
potential energy of the food. For all these reasons it seems likely 
that any attempt to compute general factors for the metab- 
olizable energy of the crude nutrients of feeding-stuffs similar to 
those of Rubner or Atwater for the nutrients of human foods would 
be confronted by almost insuperable difficulties. 

It was natural, then, to attempt to eliminate these difficulties 
by computing the results upon the digestible nutrients of the feed- 
ing-stuffs, but even here considerable difficulties arise. The di- 
gested nutrients, particularly in the case of coarse fodders, are far 
from being the pure protein, carbohydrates, and fats which our 
ordinary statements of composition and digestibility assume them 
to be. Furthermore, a considerable and a variable proportion of 
the waste of proteid metabolism in the herbivora takes the form of 
hippuric acid, a body less completely oxidized than urea, and ac- 



284 PRINCIPLES OF ANIMAL NUTRITION. 

cordingly containing more potential energy, while the urine of 
sheep and cattle also contains not a little non-nitrogenous matter 
of some sort. Finally, the slow and complicated process of diges- 
tion in the herbivora is accompanied by fermentations and the 
evolution of gaseous hydrocarbons (methane), and perhaps of 
hydrogen, both of which carry off a more or less variable propor- 
tion of the potential energy of the food. By means of experiments 
with approximately pure nutrients it is possible to secure factors 
for the metabolizable energy of the digested nutrients of con- 
centrated feeding-stuffs, but in the case of coarse fodders about 
all that is practicable in this direction is to compute the results 
of experiments upon the total digestible matter. 

There is possible, however, a third method, viz., to compute the 
metabolizable energy upon the total organic matter of the feeding- 
stuff, expressing it either as Calories per gram or pound of organic 
matter or as a percentage of the gross energy. In the latter form 
the result would be analogous to a digestion coefficient and would 
show what proportion of the total energy of the material, as- deter- 
mined by combustion in the calorimeter, was capable of being met- 
abolized in the body. This method of expressing the results has 
certain advantages in directness and simplicity, and especially in 
putting the whole matter on the basis of energy values. In the 
succeeding paragraphs the available data will be considered from 
both the standpoints last named. 



METABOLIZABLE ENERGY OF ORGANIC MATTER. 

For a discussion of the matter from this standpoint we have to 
rely almost entirely upon the Mockern investigations already men- 
tioned. In the case of those earlier experiments in which the ration 
consisted exclusively of a single coarse fodder the computation of 
the metabolizable energy of the latter is, of course, readily made. 
In the experiments in which the food under investigation was added 
to a basal ration the computation is somewhat less simple, it being 
then necessary to compare the gross energy of the added food with 
the increase in the energy of the excreta in the second period as 
compared with the first. The details of both methods will be best 
explained by illustration. 



THE FOOD AS A SOURCE OF ENERGY. 285 

Total Organic Matter. 

Coarse Fodders. Fed Alone. — For Ox H, fed exclusively on 
meadow hay, Kellner obtained the following results * per day and 
head: 

Ingesta. 

7 ; 263f grams meadow hay 32,177 . 3 Cals. 

Excreta. 

2,547 f grams feces 11,750.3 Cals. 

13,675 " urine 1,945.0 " 

158.4 " methane 2,113.7 " 

Total excreta 15,809.0 " 

Difference 16,368.3 " 

Had the ration exactly sufficed for the maintenance of the ani- 
mal, the difference of 16,368.3 Cals. would represent exactly its 
metabolizable energy. In reality, however, the nitrogen and car- 
bon balance indicated a gain by the animal of 37.2 grams of protein 
(NX 6.00 J) and 140.8 grams of fat, equivalent to 1548.8 Cals., so 
that the amount of energy actually converted into the kinetic form 
was 16,368.3-1548.8 = 14,819.5 Cals. The potential energy of the 
140.8 grams of fat, however, while it was not actually rendered 
kinetic, might have been had the needs of the organism required it. 
Its retention in the potential form was, in a sense, temporary and 
accidental, and its energy should properly be considered as a part 
of the metabolizable energy of the food. 

With the gain of protein, however, the case is different. Its 
total potential energy equals 211.2 Cals., but not all of this is 
capable of conversion into kinetic energy. According to Rubner's 
results (p. 275) each gram of urinary nitrogen derived from the met- 
abolism of the protein of lean meat corresponds to 7.45 Cals. If 
this result is applicable to the forms of protein consumed by her- 
bivora (and we shall see later that there is good reason to believe 
that such is approximately the case), then the metabolism of the 
37.2 grams of protein gained would have added 46.2 Cals. to the 
observed potential energy of the urine, while the remaining 165 
Cals. would have taken the kinetic form and should, therefore, be 
regarded as part of the metabolizable energy of the food. 

* Loc. cit., 53, 9. f Dry matter. % Compare pp. 67, 68. 



286 



PRINCIPLES OF ANIMAL NUTRITION. 



In other words, to get at the actual metabolizable energy of the 
ration in this experiment we must add to the observed potential 
energy of the urine the amount of 46.2 Cals. by which it would have 
been increased had all the protein of the food been metabolized, or, 
what is the same thing, must subtract this amount from the ob- 
served difference between food and excreta. This leaves 16,322.1 
Cals. as the metabolizable energy of 7263 grams of dry matter or 
6750 grams of organic matter in meadow hay, and the metabolizable 
energy per gram of organic matter is therefore 2.418 Cals. 

Computed in the above manner, the several experiments of this 
category gave per day and head the following results : 





! 

Ration. 


d 
a 

W 

<D 


Energy of 


Metabolizable 
Energy. 


Ani 
mal. 


Food 


Feces. 


Urine 
(Cor- 


Meth- 


Total, 


Per 
Grm. 
Or- 






'8 
Si 


Cals. 


Cals. 


rected). 
Cals. 


Cals. 


Cals. 


Mat- 
ter, 






O 
6750 












Cals. 


A 




32177.3 


11750.3 


1991.2 


2113.7 


16322.1 


2.418 


II 


' A 


7816 


36975 . 1 


15524.1 


1925.7* 


3137.2 


16388 . 1 


2.097 


V 


" B 


7199 


34211.5 


15312.2 


1559.3* 


2268 . 5 


15071.5 2.093 


VI 


■' " •' 


7125 


33855.4 


13765.2 


1737.9* 


2480.6 


15871. 712.228 


XX 


" M 


7809 


37167.3 


13880.7 


3224 . 6 


2646 . 1 


17415.9 2.230 


1 


"11 


6815 


32252 . 2 


14669.0 


1686.9 


2092 . 3 


13804.0 


2.026 






















2 . 182 


B 


Meadow hay and oat straw. . . 


7107 


33794.4 


14576.1 


1440.3 


2331.2 


15446.8 


2.173 


III 


Clover 


7X28 


34603 . 2 


15505.1 


1549.6* 


2670 . 1 


14878.4 


2.031 


IV 




7074 


33405 . 1 


15250.6 


1481.5* 


2491.3 


14181.7 


2.004 



* Energy of urine computed from its carbon content. 



It should be noted that the figures for the energy of the feces in 
these and in all the succeeding experiments include that of the met- 
abolic products contained in them. While the latter are not derived 
directly from the food they are a part of the expenditure made by 
the body in the digestion of the food, and there is. therefore, the same 
reason for including their energy as for including that of the organic 
matter of the urine. 

Both contain a certain amount of potential energy, derived 
ultimately from the food, which has escaped being metabolized in 



THE FOOD AS A SOURCE OF ENERGY. 



287 



the body and so is to be deducted from the total energy of the 
food to obtain its metabolizable energy. 

Experiments on timothy hay made by the writer,* in which the 
amount of methane excreted was estimated from the amount of non- 
nitrogenous nutrients digested, gave the following results, the cor- 
rection for the gain or loss of nitrogen being computed in a slightly 
different way from that explained above : 



ENERGY PER GRAM ORGANIC MATTER. 





Experiment I. 
Cals 


Experiment II. 
Cals. 


Experiment VI. 
Cals. 


Steer 1 


2.104 
2.007 
1.904 


1.838 
2.164 
1.824 


2.139 


" 2 


2.175 


" 3 


2.176 






Average 


2.005 


1.942 


2.163 






Average of all 




2.037 









It should be noted that the above figures are, as already stated, 
approximate only. The energy of the methane was estimated, while 
the determinations of the energy of the urine were not, in all cases, 
satisfactory. We are probably justified, however, in regarding 
the results as a close approximation to the truth. 

Coarse Fodders Added to Basal Ration. — As an example of 
this class of experiments we may take Periods 4 and 7 with Ox H.f 
The rations in the two periods were as follows : 





Total Weight. 


Containing Organic Matter. 




Period 4, 
Kgs. 


Period 7, 
Kgs. 


Period 4, 
Grms. 


Period 7, 
Grms. 


Difference, 
Grms. 


Meadow hay 

Molasses-beet pulp 

Peanut meal 


4 
3 

1 


8 
3 
1 


3198 

2386 

818 


6495 

2413 

835 


3297 

27 
17 








8 


12 


6402 


9743 


3341 



* Penna State Experiment Station, Bull 42, p. 153. 
■\Loc cit,, 53,278-335. 



PRINCIPLES OF ANIMAL NUTRITION. 



The potential energy of food and excreta (that of the urine cor- 
rected to nitrogen equilibrium) and by difference the amounts of 
metabolizable energy were: 





Food, 
Cals. 


Feces. 
Cals. 


Urine 

(Corrected), 

Cals. 


Methane, 
Cals. 


Metaboliz- 
able Energy. 
Cals. 


Period 7 

" 4 


46,275.0 
30,338.1 


14,104.8 
8,574 . 9 


2,593.0 
1,795.0 


3,564.2 

2,579.4 


26,013.0 
17,388.8 


Difference .... 


15,936.9 


5,529.9 


798.0 


984.8 


8,624 . 2 



The metabolizable energy of the additional 3341 grams of or- 
ganic matter eaten in Period 7 was therefore 8624.2 Cals. This 
added food was intended to consist of hay, but the unavoidable 
variations in the moisture content of the feeding-stuffs resulted in a 
slightly greater consumption of the other ingredients of the ration 
also. Of the 3341 grams of additional organic matter, 3297 grams, 
as the previous table shows, were from the hay and 44 grams from 
the basal ration. If, then, we would ascertain the metabolizable 
energy of the added hay only, we must subtract from the difference 
of 8624.2 Cals. between the two rations the metabolizable energy of 
this 44 grams of organic matter from the other feeding-stuffs. 

But while the gross energy of the latter is known, its metabo- 
lizable energy cannot be computed exactly, since it is impossible to 
determine what part of the energy of the excreta was derived from 
this particular portion of the ration. By assuming, however, that 
the same percentage of its gross energy was metabolizable as was 
the case with the basal ration, and that its non-metabolizable energy 
was similarly distributed between the various excreta, we may 
compute a correction which, although not strictly accurate, will not, 
in view of the small quantities involved, introduce any serious error. 
In this case the gross energy of the 3297 grams of organic matter in 
the added hay was 15,72S.6 Cals., and the table takes the form 
shown on the opposite page. 

As thus computed, the metabolizable energy of the 3297 grams 
of organic matter added to the basal ration in the form of hay was 
8504.8 Cals., equal to 2.580 Cals. per gram. The total correction 
amounts to 119.4 Cals., and even a considerable relative error in it 
would not materially change the final results. 



THE FOOD AS A SOURCE OF ENERGY. 



289 





Food, 

Cals. 


Feces, 
Cals. 


Urine 

(Corrected), 

Cals. 


Methane, 
Cals. 


Metaboliz- 

able Energy, 

Cals. 


Period 7 

" 4 


46,275.0 
30,338.1 


14,104.8 
8,574.9 


2,593 . 
1,795.0 


3,564.2 
2,579.4 


26,013.0 
17,388.8 


Difference .... 
Correction .... 


15,936.9 5,529.9 
-208.3 -58.9 


798.0 
-12.3 


984.8 8,624.2 
-17.7 -119.4 


Percentages. . . 


15,728.6 
100.0 


5,471.0 785.7 
34.78 5.00 


967.1 8,504.8 
6.15 54.07 



In these computations it is assumed that the increased metabo- 
lizable energy of the ration is derived entirely from the added feed- 
ing-stuff, or, in other words, that the latter exerted no influence 
either upon the digestibility of the basal ration or upon the propor- 
tion of its energy lost in urine and in hydrocarbons. That such is 
the case we have no means of proving, and it is, indeed, unlikely 
that it is exactly true. The metabolizable energy of the added 
feeding-stuff as above computed includes any such effects — that is, it 
represents the net result to the organism of the added coarse fodder. 

Table I of the Appendix contains the results of all the experi- 
ments of this sort, computed in the manner illustrated above. It 
will be noted that in all but two cases the correction is less than 
in the above example. In each case the table shows also the per- 
centage of the gross energy of the feeding-stuff which was found to 
be metabolizable and the percentage carried off in each of the 
excreta. 

Summary. — The results of the foregoing determinations of the 
metabolizable energy of the organic matter of coarse fodders are 
summarized in the table on page 290, which shows the gross and 
metabolizable energy per gram of organic matter and also the 
percentage of gross energy found to be metabolizable. 

Concentrated Feeding-stuffs. — The metabolizable energy of 
the organic matter of a concentrated feeding-stuff when added to 
a basal ration can, of course, be computed by the same method as in 
the case of added coarse fodders, but, as we shall see, some special 
difficulties arise in its application. 

The only commercial concentrated feeding-stuff upon which 
such experiments have been reported is beet molasses, although 



290 



PRINCIPLES OF ANIMAL NUTRITION. 



Meadow Hay : 

Sample I 

" A 

" B, Ox V. 
" B, "VI. 



B, average. 

M 

II 

V, OxF... 
V, " G... 



V, average 

VI, Ox H, Period 2. 
VI, " H, " 7. 
VI, "J 



" VI, average 

Average of seven samples 
Timothy Hay (approximate) . . 



Oat Straw : 
Ox F . . . 
" G.... 



Average. 

Wheat Straw : 

OxH 

" J 



Average. 



Extracted Rye Straw , 

OxH 

" J 



Per Gram Organic 
Matter. 



Gross 
Energy, 

Cals. 



4.767 
4.731 

4.752 



4.760 
4.734 

1 4. 743 J 



4.771 



4.751 
4.670 

I 4.816 I 



1 4.743 J 



4.251 J 



Metaboliz- 

able 

Energy, 

Cals. 



Per Cent. 

Metaboliz- 

able. 



2.418 
2.097 
2.093 

2.228 



2.161 

2.230 
2.026 
1 . 933 

2.087 



2.010 

2.520 
2 . 580 
2.540 



2.547 



2.213 

2.037 



1.760 
1.688 



1.724 



1.411 
1.540 



1.475 



3.261 
3.164 



Average | | 3.213 



50.72 
44.32 
44.06 
46.88 



45.47 

46.86 
42.80 
40.75 
44.00 



42.38 

52.82 
54 . 07 
53.24 



53.38 



46.56 
43.62 



36.54 
35.05 



35.80 



29.75 
32.47 



31.11 



76.71 
74.45 



75.58 



experiments were also made by Kellner with wheat gluten, starch, 
oil, and extracted straw, the aim of which was to determine the 
metabolizable energy of the various digestible nutrients. 

As an illustration of this class of experiments we may take one 
upon molasses with Ox F,* comparing Period 3, on the basal ration, 
* Loc. cit., 53, 172-227. 



THE FOOD AS A SOURCE OF ENERGY. 



291 



with Period 6, on the same ration with the addition of molasses. 
Comparing, first, the organic matter of the two rations we have 
the following: 





Total Organic 

Matter Fed, 

Grms. 


Organic Matter in 

Molasses, 

Grms. 


Period 6 


8262 
6630 

1632 


1702 


" 3 







1702 



In the period with molasses 70 grams less of the basal ration 
was consumed than in the period without, and a correction must 
accordingly be made for this in the way explained on page 288. 
The energy of food and excreta in the two experiments (that 
of the urine being corrected to nitrogen equilibrium), together with 
the correction for the 70 grams of organic matter, is shown in the 
following table : 





Food, 
Cals. 


Feces, 
Cals. 


Urine, 
Cals. 


Methane, 
Cals. 


Metaboliz- 

able Energy, 

Cals. 


Period 6 

" 3 


37,946.2 
31,327.8 


11,365.8 
9,599.2 


1,786.1 
1,530.0 


2,397.9 
2,560.7 


22,396.4 
17,637.9 


Correction 


6,618.4 
+ 330.8 


1,766.6 
+ 101.3 


256.1 
+ 16.2 


-162.8 
+ 27.0 


4,758.5 
+ 186.3 




6,949.2 


1,867.9 


272.3 


-135.8 


4,944 . 8 



Dividing the metabolizable energy of the molasses, 4944.8 Cals., 
by the number of grams consumed, 1702, gives the metabolizable 
energy of 1 gram of organic matter as 2.905 Cals. 

Real and Apparent Metabolizable Energy. — The above 
figures, however, demand more critical discussion. While the addi- 
tion of molasses to the basal ration increased the amount of poten- 
tial energy carried off in the feces and urine, it diminished that in 
the methane; that is, it acted in some way to check the fermen- 
tation in the digestive tract to which this gas owes its origin. In 
other words, under the influence of the molasses the loss of energy 
by fermentation of the basal ration was diminished by 135.8 Cals., 
and this amount, by the method of computation, is added to the 
metabolizable energy of the molasses. 



292 



PRINCIPLES OF ANIMAL NUTRITION. 



Moreover, the loss of energy in the feces is a complex of sev- 
eral factors. The amounts of organic matter and of the several 
nutrients excreted in the feces in the two periods (not corrected for 
the 70 grams difference in organic matter consumed) were as 
follows : 





Organic 
Matter, 
Grms. 


Protein, 
Grms. 


Crude 

Fiber, 
Grms. 


Nitrogen- 
free 
Extract, 
Grms. 


Crude 

Fat, 

Grms. 


Period 6 


2132 

1797 


403 
284 


595 
527 


1068 66 


" 3 


924 62 






Difference 


335 


119 


68 


144 


4 







In addition to protein and nitrogen-free extract, which may 
possibly represent indigestible material in the molasses, the feces 
contained 68 grams more crude fiber and 4 grams more fat in Period 
6 than in Period 3. These cannot have been derived from the 
molasses, since the latter does not contain these ingredients. This 
feeding-stuff, in other words, diminished the apparent digestibility 
of the fiber and fat of the basal ration. As a matter of fact, the 
ingredients of molasses being practically all soluble in water, it is 
probable that nearly all the difference in the amount digested is 
due to the diminished apparent digestibility of the basal ration 
under the influence of the molasses. 

The figure above given for the metabolizable energy includes all 
these effects; that is, it shows the net result as regards energy ob- 
tained from molasses fed under the conditions of these experiments, 
the nutritive ratio of the basal ration being 1 : 5.8 and that of the 
molasses ration 1 : 6.4. To get at the actual amount of energy set 
free from the molasses itself we should need to subtract from the 
metabolizable energy as calculated above the energy corresponding 
to the decreased excretion of methane and to add to it the metabo- 
lizable energy corresponding to the decrease in the amounts of crude 
fiber and ether extract digested, assuming that all the excess of 
protein and nitrogen-free extract in the feces was derived from the 
molasses. Computed in this way * the real metabolizable energy 



* One gram of crude fiber =3.3 Cals., and one gram of ether extract = 
8.3 Cals. See p. 332. 



THE FOOD AS A SOURCE OF ENERGY. 293 

of the organic matter is 2.977 Cals. per gram. This would be a mini- 
mum figure, while if we assume, as suggested above, that the mo- 
lasses is entirely digestible, this figure is still too low and should be 
increased to equal the gross energy of the organic matter. 

If, however, either one of these latter values were used in com- 
puting the metabolizable energy of rations, the results would obvi- 
ously be too high unless corrections were made for the effect upon 
the apparent digestibility of the other feeding-stuffs in the ration. 
The figure first computed, while including several different effects, 
nevertheless seems better adapted for use in actual computations 
under average conditions, while the second gives the more accurate 
idea of the store of metabolizable energy contained in the feeding- 
stuff regarded by itself. The distinction is analogous to that 
between apparent and real digestibility, and we may accordingly 
speak of the apparent and the real metabolizable energy of feeding- 
stuffs. 

The whole of our present discussion of the metabolizable 
energy of the organic matter (total or digestible) of food materials 
relates to the apparent metabolizable energy. This is obvious as 
regards the concentrated feeds from the above example, and logic- 
ally applies also to those cases in which coarse fodders were added 
to the basal ration, while in the case of the coarse fodders used alone 
the distinction vanishes or is reduced to one between apparent and 
real digestibility. The experiment with beet molasses well illus- 
trates the difficulties in the way of determining the actual metabo- 
lizable energy of feeding-stuffs which cannot be used alone. 

Beet Molasses.— In two later experiments the addition of 
molasses increased instead of diminishing the excretion of methane. 
The results of the three experiments upon molasses, computed in 
the same manner as the experiments upon coarse fodders, are con- 
tained in Table II of the Appendix. 

In the last two experiments 10 to 12 per cent, of the energy of 
the molasses was lost in the products of intestinal fermentation, 
but this was more than counterbalanced by its less effect upon the 
digestibility of the rations, so that the final result is a higher figure 
for the apparently metabolizable energy than in the first experi- 
ment. Summarizing the results per gram as in the case of the 
coarse fodders we have: 



294 



PRINCIPLES OF ANIMAL NUTRITION. 





Gross 

Energy, 

Cals. 


Apparently 

Metabolizable 

Energy, 

Cals. 


Per Cent 
Metabolizable. 


Sample I.. . , 


4.084 

i 4 . 188 


1 


2.905 
3.308 
3.044 


71 . 16 


" II, Ox H 


79.00 


" " "J 


72.70 








3.176 


75.85 









Starch. — In a considerable number of the trials commercial 
starch was added to the basal ration. The earlier experiments by 
Kiihn were intended primarily to throw light on the possible for- 
mation of fat from carbohydrates (compare p. 177). In them, 
starch was added to a ration of coarse fodder only and the nutritive 
ratio was purposely made very wide, the result being that more or 
less of the starch escaped digestion. In the later experiments by 
Kellner the starch was added to a mixed ration. Except in the 
first two experiments the nutritive ratio was a medium one and 
but traces of starch escaped digestion. It will be convenient, 
therefore, to tabulate these two classes of experiments separately, 
as has been done in Tables III and IV of the Appendix, the com- 
putations being made as in the previous cases. 

The same remarks which were made on p. 291 concerning the 
distinction between real and apparent metabolizable energy apply 
to these results. As computed they represent the net gain to the 
organism from the consumption of starch and are the algebraic sum 
of several factors. In particular, there was a considerable loss of 
energy in the feces, even in the later experiments in which but 
traces of the starch itself escaped digestion. In other words, the 
starch either lowered the digestibility of the basal ration or in- 
creased the formation of fecal metabolic products or both. The 
method of computation adopted virtually looks upon this as part 
of the necessary expenditure in the digestion of the starch. On 
the other hand, there are several cases in which there was a de- 
crease in the outgo of potential energy in the urine, even after the 
results are corrected to nitrogen equilibrium. This, from our pres- 
ent point of view, is credited to the starch and increases its 
apparent metabolizable energy. 



THE FOOD AS A SOURCE OF ENERGY. 



2 95 



The results on starch, expressed in Calories per gram of organic 
matter, may be summarized as follows : 





Gross 

Energy, 

Cals. 


Apparent 

Metaboliz- 

able 

Energy, 

Cals. 


Per Cent. 

Metaboliz- 

able. 


Kithn's Experiments : 

Sample I, Ox III 


4.249 
4.249 


3.029 
2.705 


71.21 


" " " IV 


63.71 






Average 


4.249 

4.236 
4.236 
4.236 
4.236 


2.867 

3.347 
3.161 
3.018 
2.964 


67.46 


Sample II, Ox V, Period 2a 


78.95 


" " " " " 26 


74.68 


" " " VI, " 2b 


71.26 


a ii n u a o 


69.98 






Average 


4.236 

4.243 

4.165 
4.165 


3.123 
2.995 

2.027 
2.028 


73.72 


Average of I and II 


70.59 


Kellner's Experiments : 

Samples I and II Ox B 


48.62 


a a a u u r-f 


48.68 






Average 


4.165 

4.156 
4.156 
4.156 


2.028 

2.792 
2.969 
3.214 


48.65 


Sample III, Ox D 


67.20 


ii u a "p 


71.44 


" " G 


77.32 






Average 


4.151 

4.180 
4.180 


. 2.992 

3.313 
3.017 


71.99 


Sample IV, Ox H 


79.22 


" " J 


72.16 


Average 


4.180 
4.168 


3.165 
3.079 


75.69 


Average of III and IV 


73.84 







Wheat Gluten. — Seven experiments upon commercial wheat 
gluten are reported, three by Kiihn and four by Kellner. The 
chemical composition of the dry matter of the three samples of 
gluten employed is shown in the first table on the next page. 

In Kiihn's experiments the gluten caused a marked increase in 
the apparent digestibility of the basal ration, which by our method 
of computation augments the apparent metabolizable energy of 
the gluten, so that in one case it amounts to over 101 per cent, of 
the gross energy. The correction for organic matter i9 also rela- 



296 



PRINCIPLES OF ANIMAL NUTRITION. 





Kiihn's 

Experiments. 

Per Cent. 


Kellner's Experiments. 




Oxen B and C, 
Per Cent. 


Ox D, 
Per Cent. 


Ash 


1.36 

87.88 
0.47 
8.07 
2.22 


2.86 
83.45 

0.08 
13.35 

0.26 


2 80 


Crude protein 


82 67 


Crude fiber 


43 


Nitrogen-free extract 


13 38 


Ether extract 


72 








100.00 


100.00 


100.00 



lively large. In Kellner's experiments the variations are not so 
great. Computed as before, the results are as shown in Table V of 
the Appendix. Summarizing Kellner's figures, as probably the 
more accurate, we have per gram of organic matter — 





Gross Energy. 

Cais. 


Apparent 

Metabolizable 

Energy. 

Cals. 


Per Cent. 
Metabolizable. 


Sample I, Ox B, Period 1 . . . . 
" " " " " 3.... 
" " " C 


5.675 
5.675 
5.675 


3.019 
3.719 
4.062 


53.18 

65.55 
71 61 






Average 

Sample II, Ox D 


5.675 
5.808 
5.742 


3.600 
4.061 
3.831 


63.45 
69 90 


Average of I and II 


66 68 







The wheat gluten was by no means pure protein and the above 
figures of course apply to the feeding- stuff as a whole, including its 
fat and carbohydrates as well as its protein. The question of the 
metabolizable energy of the latter will be considered subsequently. 

Peanut Oil. — Three experiments with this substance are re- 
ported by Kellner. In the first the oil was given in the form of an 
emulsion, prepared by saponifying a small portion of the oil with 
sodium hydrate, and was completely digested In the second and 
third experiments it was emulsified with lime-water. In this form 
it was less well digested, and in one case (Ox F) affected the digesti- 
bility of the basal ration unfavorably. The results per gram of 
organic matter, computed as before, constitute Table VI of the 
Appendix and are summarized in the following table: 



THE FOOD AS A SOURCE OF ENERGY. 



297 





Gross Energy, 
Cais. 


Metabolizable 

Energy, 

Cals. 


Per Cent. 
Metabolizable. 


" 11, " F 

" " " G 


9.493 
I 9.464 | 


7.382 
4.973 
5.623 


77.76 
52.52 
59.39 




5.298 


55.96 









Summary. — The foregoing results may be conveniently sum- 
marized in the table below, which shows the average gross energy 
per gram of organic matter, the percentage of this gross energy 
carried off unmetabolized in the various excreta, and the apparent 
metabolizable energy expressed both per gram of total organic 
matter and as a percentage of the gross energy : 











Apparent 




Cross 


Percentage Loss in 


Metabolizable 




En'gy 






Energy. 














Grm. 














Or- 








Per 






ganic 








Grm. 


Per 




Mat- 








Or- 


Cent. 




ter, 


Feces. 


Urine. 


Methane. 


ganic 


of 




Cals. 








Mat- 
ter, 
Cals. 


Gross 
En'gy. 






40.96 


5.71 


6.77 


2.213 


46.56 


Timothy hay 


4.670 


47.27 


2.61 


6. 50* 


2.037 


43.62 


Oat straw 


4.816 
4.743 
4.251 

4.188 


56.80 

58.22 

12.75 

9.93 


2.08 

2.37 

-0.79 

2.91 


5.32 

8.30 

12.46 

11.31 


1.724 
1.475 
3.213 
3.174 


35.80 




31.11 


Extracted rye straw 


75.58 




75.85 




4.243 


19.59 


-0.92 


10.74 


2.995 


70.59 


' ' Kellner's experiments: 
















4.165 
4.168 


55.91 
17.61 


-2.07 
-0.66 


-2.49 
9.21 


2.028 
3.079 


48.65 




73.84 


Wheat gluten, Kellner's experi- 




ments 


5.742 
9.493 
9.464 
9.464 


20.16 

24.34 
64.77 
41.00 


13.08 

-1.08 

-1.19 

1.37 


0.08 

-1.02 

-16.10 

-1.76 


3.831 
7.382 
4.973 
5.623 


66.68 


Peanut oil, Ox D 


77.76 


« <. u -p 


52.52 


" " " G 


59.39 







* Estimated. 

Digestible Organic Matter. 
As appears especially from the figures of the last table, the loss 
of energy in the feces is the one which is subject to the greatest vari- 
ation. In other words, the digestibility of a feeding-stuff is the 



;a8 



PRINCIPLES OF ANIMAL NUTRITION. 



most important single factor in determining its content of metabo- 
lizable energy. We may eliminate this factor by computing, on 
the basis of the determinations of digestibility, the energy of the 
digested organic matter and the proportion of this energy which 
was lost in urine and methane or was metabolizable. In this way 
we may secure figures which will be useful as a basis for estimat- 
ing the energy values of rations in experiments in which it has 
not been determined, and which will also afford, from some points 
of view, a better idea of the relative extent of the losses other than 
those in the feces. 

Coarse Fodders Alone. — In the cases in which coarse fodder 
constituted the exclusive ration the computation from the data 
given on p. 286 and the amounts of organic matter apparently 
digested in the several experiments is very simple and yields the 
following results per gram digested organic matter: 



Ani- 
mal. 



A 

II 

V 

VI 

XX 

I 



Feed. 



Meadow hay I . 
A. 
B. 
B, 
M. 
II. 



Average 

Average for timothy hay 



Gross 
Energy. 



4.509 
4.408 
4.317 
4.398 
4.452 
4.371 



4 . 409 
4.377 



Loss in 



Urine, 
Per 
Cent. 



9.75 

8.98 
8.25 
8.65 
13.85 
9.59 



9.85 
4.95 



Methane 

Per 

Cent. 



10.35 
14.62 
12.00 
12.35 
11.36 
11.90 



12.09 
12.33 



Metabolizable 
Energy. 



Per 

Cent. 



79.90 

76.40 
79.75 
79.00 
74.79 
78.51 



78.06 

82.72 



Per 
Grm. 

Cals. 



3.603 
3.368 
3 . 443 
3.474 
3.330 
3.432 

3.442 
3.620 



Coarse Fodders Added to Basal Ration. — From the re- 
sults contained in Table I of the Appendix we may compute in sub- 
stantially the same manner the total and metabolizable energy of 
the digestible organic matter of the coarse fodders which were 
added to the basal rations. In the table referred to, a correction 
was introduced for the small differences in the amount of the basal 
rations consumed in the periods compared. In the present com- 
putations it has been assumed that the organic matter of these 
small differences possessed the same digestibility as the total organic 
matter of the basal ration. For example, in the case of Ox H, 



THE FOOD AS A SOURCE OF ENERGY. 299 

Periods 4 and 7, the amounts of digestible organic matter in the 

two rations were : 

Period 7 7106 grams 

Period 4 4845 " 

Difference 2261 " 

The table shows, however, that in Period 7 the animal received 44 
grams more of total organic matter in the basal ration than in 
Period 4. In the latter period the digestibility of the organic 
matter was found to be 75.7 per cent. Consequently, of the 
excess of 2261 grams of digestible organic matter in Period 7 
44x0.757 = 33 grams maybe regarded as derived from the basal 
ration and 2261 — 33 = 2228 grams from the meadow hay added. 
The corresponding corrected amounts of energy as given in the 
same table are — 



Total Cals. 



Per Grm. Digested 

Organic Matter 

Cals. 



Energy of added hay (corrected) 
'"' " corresponding feces. . . 

" " digested matter 

Metabolizable energy 



15728.6 
5471.0 

10257.6 
8504.8 



4.604 
3.817 



The table on the next page contains the results of these com- 
putations expressed per gram of digested organic matter. Kell- 
ner* has made the same comparison in a slightly different man- 
ner. His results for the gross energy of the digested matter are 
given subsequently (p. 310). Those for metabolizable energy do 
not differ materially from those here given. 

Concentrated Feeding-stuffs. — The results of experiments 
upon concentrated feeding-stuffs may of course be computed in the 
same manner as those upon coarse fodders just considered. In the 
case of materials like starch, oil, and gluten, however, which differ 
widely from ordinary feeding-stuffs and which produce material 
and readily traceable effects upon the digestibility of the basal 
ration, relatively little value attaches to computations of the appar- 
ent metabolizable energy, and only the average results with these 
materials have been included in the summary on page 301 for the 
* Loc. cit,, 53, 414 and 447. 



3°° 



PRINCIPLES OF ANIMAL NUTRITION. 



*e3 


-6 

'u 
Ph 




Total 

Energy, 

Cals. 


Loss in 


Apparent 

Metabolizable 

Energy. 


s 

q 
< 


Urine. 
Per Cent. 


Methane, 
Per Cent. 


Per Cent. 


Per Grm.. 
Cals. 


F 
G 


1 

2 

2 

7 
2 

2 

1 

I 
I 

5 
5 


Meadow Hay : 

Sample V 

V 

Average 

Sample VI 

" VI 

" VI 

Average 

Oat Straw : 

Sample 11 

" II 

Average 

Wheat Straw : 

Sample I 

" I 

Average 

Extracted Straw : 

Sample I 

" I 

Average 


4.356 
4.496 


8.61 

7.72 


10.20 
12.58 


81.19 

79.70 


3.537 
3.583 


H 
H 
J 


4.426 

4.531 
4.604 
4.506 


8.17 

8.32 
7.66 
9.64 


11.39 

7.74 
9.43 
9.33 


80.44 

83.94 
82.91 
81.03 


3.560 

3.803 
3.817 
3.651 


F 
G 


4.547 

4.441 

4.586 


8.54 

5.30 
4.32 


8.83 

10.17 
14.42 


82.63 

84.53 
81.26 


3.757 

3.754 
3.726 


H 
J 


4.514 

4.488 
4.397 


4.81 

4.75 
6.49 


12.30 

20.11 
19.67 


82.89 

75.14 

73.84 


3.740 

3.373 
3.247 


H 
J 


4.443 

4.240 
4.164 


5.62 

-0.52 
-1.29 


19.89 

13.99 

14.58 


74.49 

86.53 
86.71 


3.310 

3.668 
3.611 




4.202 


-0.91 


14.29 


86.62 


3.640 



sake of completeness. Those upon peanut oil have been omitted, 
since the varying effect upon digestibility and upon the methane 
fermentation makes the results as computed in this way appear 
of questionable significance. 

Summary. — The average results upon the various materials 
experimented with are summarized on the opposite page. 

As appears from the figures of the table, the apparent metabo- 
lizable energy of the digestible organic matter of the different coarse 
fodders is quite uniform. At first sight it appears somewhat sur- 
prising that oat straw should show more favorable results than hay, 
but the reason is readily seen in the smaller loss which takes place 
in the urine ; in wheat straw this loss is somewhat larger, while that 



THE FOOD AS A SOURCE OF ENERGY. 
ENERGY OF DIGESTED ORGANIC MATTER. 



301 





Loss in 


Total 

Energy. 

Cals. 






Urine, 
Per 
Cent. 


Methane, 

Per 

Cent. 


4.439 


9.62 


11.52 


4.377 


4.95 


12.33 


4.514 


4.81 


12.30 


4.443 


5.62 


19.89 


4.202 


-0.91 


14.29 


4.124 


3.24 


12.52 


4.192 


-1.19 


13.42 


4.012 


-0.92 


11.12 


5.749 


16.59 


0.02 



Apparent 

Metabolizable 

Energy. 



Per 
Cent. 



Per 
Grm., 
Cals. 



Meadow hay (seven samples) 

Timothy hay 

Oat straw 

Wheat straw 

Extracted straw 

Beet molasses, Sample II 

Starch, Kiihn's experiments 

" Kellner's experiments * 

Wheat gluten, Kellner's experiments.. 



78.86 
82.72 
82.89 
74.49 
86.62 
84.24 
87.77 
89.80 
83.39 



3.501 
3.620 
3.740 
3.310 
3.640 
3.473 
3.679 
3.603 
4.792 



* Average of Samples III and IV. 
in the methane is considerably larger, resulting in a materially 
lower figure for metabolizable energy. 

The results summarized in the two preceding tables, it should 
be remembered, include, as already pointed out, all the effects pro- 
duced by the addition of the material under experiment to the 
basal ration; that is, they give the apparent metabolizable energy. 
In the case of the coarse fodders no other method of computation 
is practicable, and the same would be true in most instances of 
ordinary concentrated commercial feeding-stuffs. In such cases it 
is rarely possible to distinguish with accuracy between the energy 
derived from the material experimented with and the subsidiary 
effects of the latter upon the digestibility of the several in- 
gredients of the ration or upon the losses of energy in urine and 
methane. We may anticipate, therefore, that the results of future 
determinations of the metabolizable energy of ordinary feeding- 
stuffs will of necessity be expressed substantially in the summary 
manner here employed. 

With the nearly pure nutrients used in many of Kellner's ex- 
periments the case is different. Here it is possible to take account, 
to a large degree, of the secondary effects, such as those, for exam- 
ple, which in the case of wheat gluten result in figures exceeding 
100 per cent, for the apparent metabolizable energy, and to compute 
results which represent more nearly the actual metabolizable energy 
contained in the substances themselves. In these cases, therefore, 



3° 2 



PRINCIPLES OF ANIMAL NUTRITION. 



the averages of the tables are of less significance than the results 
given in the following pages, where the digestible nutrients are 
made the basis of the computation. 

ENERGY OF DIGESTIBLE NUTRIENTS. 

The foregoing paragraphs have dealt with the apparent 
metabolizable energy of feeding-stuffs, and the results have 
been expressed in terms of total or of digestible organic matter, 
or as percentages of gross energy. We now turn to a con- 
sideration of such data as are available regarding the several con- 
ventional groups of nutrients into which the food of herbivorous 
animals is ordinarily divided and inquire whether it is possible to 
compute average factors for their metabolizable energy which 
shall be useful in themselves and be of value particularly for pur- 
poses of comparison with earlier experiments. This was the special 
purpose of Kellner's investigations, and his experiments supply 
valuable data on these points as regards cattle and presumably 
other ruminants, which may be supplemented to a certain extent 
from experiments by other investigators upon horses and swine. 
In considering the experiments from this standpoint, Kellner's 
discussion and methods of computation have been closely followed, 
the attempt being made to compute as accurately as possible the 
real metabolizable energy of the several nutrients. 

Gross Energy. 
If it were possible to add pure nutrients to a basal ration and 
be sure that they would have no effect upon the utilization of the 
latter, it would be a comparatively simple matter to determine their 
real metabolizable energy. As a matter of fact, however, as has 
been seen, this is not possible. Not only is it impracticable to secure 
large quantities of pure nutrients, but each such addition to the basal 
ration is liable to affect especially the digestibility of the latter. 
Consequently the difference in metabolizable energy between the 
two rations fails to represent correctly the real metabolizable energy 
of the nutrient added. In order to compute the latter we must 
have a basis for correcting the results for the small variations in the 
amounts of other nutrients digested, and for this purpose we need 
to know the total or gross energy of the digested matters. 



THE FOOD AS A SOURCE OF ENERGY. 



3°3 



Crude Fiber. — In four of his experiments on hay fed alone, 
Kellner * determined the heats of combustion of the crude fiber of 
the food and of the feces with the following results per gram : 





Crude Fiber of 
Hay, Cals. 


Crude Fiber of 
Feces, Cals. 


I.... 

II.... 

III.... 

IV.... 


4.4350 
4.3907 
4.4548 
4.4230 


4.7378 
4 . 7423 
4.9037 

4 . 7426 



It appears from these figures that the crude fiber of meadow 
hay has a higher heat value than pure cellulose (4.1854 Cals. accord- 
ing to Stohmann), obviously due to the admixture of compounds 
richer in carbon, while the indigestible crude fiber of the feces has 
a still higher heat value. Merrill f has also reported similar results 
for the crude fiber of oat hay, clover silage, and oat and pea silage, 
as follows: 





Crude Fiber of Fodder. 
Cals. per Grm. 


Crude Fiber of Feces. 
Cals. per Grm. 


Oat hay 


4 . 405 
4.610 
4.667 


4 . 662 
5.215 
4.820 


Clover silage 


Oat and pea silage .... 



It follows that the digested portions of the crude fiber must 
contain less potential energy than the crude fiber of the feed, and 
from the known digestibility of the latter it is easy to calculate 
what the heat of combustion of the digested portion must be. 
Kellner 's results, after deducting 5.711 Cals. per gram for the slight 
amounts of nitrogenous matter still contained in the crude fiber, 
were as shown on the next page. 

The average result shows that not only the chemical com- 
position but likewise the heat of combustion of the digested crude 
fiber varies but little from that of pure cellulose. Merrill's figures, 
computed in the same manner from the data of the digestion 
experiments reported by Bartlett,| but without the correction for 

* Loc. cit., 47,299. 

t Maine Expt. Station, Bull. 67, p. 170. 

X Ibid., pp. 140 and 150, and Report, 1898, p. 87. 



3°4 



PRINCIPLES OF ANIMAL NUTRITION. 



JI 



III 



IV 



In hay.. 
" feces . 



Digested fiber , 

Heat of combustion per gram , 



In hay . 
" feces. 



Digested fiber 

Heat of combustion per gram . 



In hay . 
feces 



Digested fiber 

Heat of combustion per gram . 



In hay. . 
" feces. 



Digested fiber 

Heat of combustion per gram . 



Average heat of combustion per gram . 



Crude 
Fiber, 
Grms. 



2832 
1034 



1798 



2394 

822 



1572 



2329 
769 



1560 



1978 
716 



1262 



Equivalent 

Energy, 

Cals. 



12532.8 
4869.2 



7663 
4 

10503 

3878, 



6 
2623 



6624 

4 

10367 
3754 



9 
2143 

7 




6613 

4 

8732 
3479 



7 
2396 


2 



5252 
4 



1623 
2196 



nitrogenous matter, give the following results per gram for the 
digested crude fiber : 

Oat hay 4. 161 Cals. 

Clover silage 4. 123 " 

Oat and pea silage ', . . 4 . 584 " 

Ether Extract. — Similar determinations by Kellner * on the 
ether extract of hay and feces yielded the following results per gram : 





Ether Extract 
of Hay, Cais. 


Ether Extract 
of Feces. Cals. 


I 

II 

III...... 

IV 
V 

Average. . 


9.1604 

I 9.3240 j 

9.0554 
9.1062 


9 . 7690 
9 . 8923 
9.8646 
9.8314 
9.7640 


9.1940 


9.8243 



* hoc. cit., 47, 301. 



THE FOOD AS A SOURCE OF ENERGY. 305 

A calculation similar to that made for the crude fiber yielded the 
following figures for the heat of combustion of the digested portion : 

1 8.239 Cals. 

II 7.802 " 

III 8.185 " 

IV 8.267 " 

V 8.685 " 

That these results are more or less discordant is not surprising 
in view of the uncertain elements involved in the determinations. 
Applying the average figures for the energy per gram of the ether ex- 
tracts to the total amounts eaten and excreted in the five experiments 
taken together, we have for the average energy of the apparently 
digested ether extract 8.322 Cals. per gram, a figure considerably 
below the results recorded on p. 238 for either animal or vegetable 
fats. It must be remembered, however, that the ether extract of 
the feces contains more or less metabolic products, so that the 
above result does not represent the actual energy of the digested 
ether extract. It does, however, represent the energy correspond- 
ing to the difference between food and feces with which we reckon 
in computing rations, and from this point of view it is of value. 

Nitrogen-free Extract. — The nitrogen-free extract cannot 
be separated and examined like the crude fiber and the ether ex- 
tract, but it is possible to arrive at an estimate of its heat of com- 
bustion indirectly. For this purpose Kellner assumes the average 
heat of combustion of the proteids (proteid nitrogen X 6.25) as 
5.711 Cals. per gram and that of the non-proteids as equal to that 
of asparagin, viz., 3.511 Cals. per gram. By subtracting from the 
gross energy of food or feces as directly determined the energy of 
the amounts of proteids, non-proteids, crude fiber, and ether ex- 
tract shown by analysis to be present, he computes the heat of 
combustion of the nitrogen-free extract. Furthermore, by compar- 
ing the results on food and feces as in the case of the crude fiber the 
heat of combustion of the digested portion may be computed. 
The results per gram of such a computation for the same four ex- 
periments were: * 

* hoc. cU., 47, 303-306. 



3° 6 



PRINCIPLES OF ANIMAL NUTRITION. 





N.-fr. Extract 

of Hay, 
Cals. per Gram 


N -fr. Extract 

of Feces, 
Cals. per Gram. 


Dip-ested N -fr. 

Extract. 
Cals. per Gram. 


I 


4.5713 
4 . 6547 
4.5029 
4 . 6081 


5.2834 
5.4212 
5.1058 
5.2484 


4.203 


II 

Ill 


4.146 
4.246 


IV 


4.335 


Average 


4.584 


5.265 


4.232 



In view of the indirect nature of the computation the results 
agree as well as could be expected and show that, as might be 
anticipated from its chemical composition, the heat of combustion 
of the digested portion of the nitrogen-free extract did not vary 
widely from that of starch. 

Digested Matter of Mixed' Rations. — The Mockern experi- 
ments afford accurate data as to the energy of the total digested 
matter of a large number of mixed rations. Kellner * has com- 
pared this with the computed energy of the same material. For 
this computation the factors used were : for fat, 8.322 Cals. per gram ; 
for crude fiber and nitrogen-free extract, the average of Stohmann's 
figures for starch and cellulose, 4.184 Cals. per gram; for protein 
provisionally, 5.711 Cals. per gram. Of the fifty-nine experiments, 
twelve, in which large amounts of wheat gluten or oil were fed, 
showed sufficient differences to indicate that the figures assumed 
for protein and fat were too low as applied to these two materials. 
In the other forty-seven cases the differences were nearly all less 
than 2 per cent, of the total amount and were in both directions. 

The special interest of these results lies in the fact that they 
show that we may safely use the above figures as indicated on p. 
302 to correct the results reached from a comparison of two rations. 

Nitrogen- free Extract of Starch. — As an example of Kell- 
ner's method of computation we may compare the results for Ox H 
in Period 3, with starch, and in Period 4, on the basal ration. The 
total energy of the apparently digested matter (compare Table 
IV of the Appendix) was — 

Period 3, with starch 28,718 Cals. 

Period 4, without starch 21 ,763 " 

Difference 6,955 " 

* hoc. cit., 53, 407. 



THE FOOD AS A SOURCE OF ENERGY. 



307 



A slightly less amount of the basal ration was eaten in Period 3 
than in Period 4. The difference in crude nutrients and in esti- 
mated digestible nutrients was as follows : 





Total, 
Grms. 


Estimated Digestible. 


Grms. 


Equivalent 
Energy, Cals. 


Protein 


4 

13) 
23 j 


2 
24 


11.4 
100.4 


Crude fiber 


Nitrogen-free extract. . . . 


111.8 



This amount of 112 Cals. should be added to the energy of 
the digested matter of Period 3 or subtracted from that of Period 4 
in order to render them comparable, thus making the real difference 
due to the starch 7067 Cals. Still further, the starch diminished 
the digestibility of the other nutrients of the ration by the following 
amounts : 





Grms. 


Equivalent 
Energy, Cals. 


Protein 


118 

17 

9 


673.8 
71.1 
74.9 




819.8 



Had these amounts been digested in Period 3 as in Period 4, the 
energy of the digested matter of the ration would have been 820 
Cals. greater, and the difference between the two periods would 
have been 7887 Cals. The digestible nitrogen-free extract was 
1876 grams more in Period 3 than in Period 4. Assuming all of 
this to be derived from the starch, we have for the energy of each 
gram of digested nitrogen-free extract 7887-^1876 = 4.204 Cals. 

The following table* contains the results of all the starch 
experiments computed in the manner just outlined: 

* Loc. tit., 53, 412. 



308 PRINCIPLES OF ANIMAL NUTRITION. 

ENERGY OF DIGESTED NITROGEN-FREE EXTRACT OF STARCH. 

Ox III 4.283 Cals. 

Ox IV..... 4.202 " 

Ox V (Period 2a) 4.380 " 

Ox V (Period 26) 4.324 " 

Ox VI (Period 2b) 4. 159 " 

Ox B 4.050 " 

Ox C 4.000 " 

Ox D 4.099 " 

Ox F 4.219 " 

OxG 4.213 " 

Ox H 4.204 " 

Ox J 4.095 " 

Average 4. 185 " 

Carbohydrates of Extracted Straw. — Computed in the 
same manner as the experiments upon starch, the two experiments 
upon this substance gave the following results : * 

OxH 4.278 Cals. 

OxJ 4.216 " 

Average . . .... 4.247 " 

This average is slightly higher than would be computed on the 
assumption that the digested crude fiber and nitrogen-free extract 
had the heat values respectively of the digested crude fiber of hay 
and the digested nitrogen-free extract of starch. 

Peanut Oil. — Four experiments upon this substance similarly 
computed give the following results; * 

OxD..,.. 8 508 Cals 

OxE 8 845 " 

OxF 8 820 " 

OxG.... 9.112 " 

Average 8 . 821 " 

*Loc cit , 53 413 and 414 



THE FOOD AS A SOURCE OF ENERGY. 309 

As in the case of the ether extract of hay, the energy of the 
digested fat is less than that of the original material, which was 
9.478 Cals. per gram. 

Protein of Wheat Gluten. — Comparing the experiments with 
and without this material exactly as in the case of the starch, we 
have the following results * for the energy of the digested protein : 

Ox B (Period 1) 5.728 Cals. 

Ox B (Period 3) 5.817 " 

Ox C (Period 3 5.712 " 

Ox D (Period 4) 6.040 " 

Ox E (Period 4) 6 . 009 " 

Ox III (Period 3) 6.166 " 

Ox III (Period 4) 6.277 " 

Ox IV (Period 3) 6.061 " 

Average •. 5. 976 " 

In these trials three different kinds of gluten were used which 
were prepared by somewhat different processes. The averages for 
the three sorts separately were as follows : 

No. 1 5.732 Cals. 

" 2 6.025 " 

" 3 6.168 " 

5.975 " 

The above figures refer to the so-called crude protein, that is, to 
nitrogen X 6.25. The proteins of wheat, however, contain con- 
siderably over 16 per cent, of nitrogen. Using Ritthausen 's factor, 
namely, 5.7, for the computation of protein from nitrogen reduces 
the amount of protein in the gluten and increases that of the 
nitrogen-free extract by the same amount. The energy of the 
digested protein when computed on this basis equals 6.148 Cals. 
per gram. 

Organic Matter of Coarse Fodders. — For the total digested 
organic matter of hay and straw the following heat values per gram 
were computed:* 

* hoc. tit., 53, 412 and 414. 



3io 



PRINCIPLES OF ANIMAL NUTRITION. 



Meadow hay I, OxA 4509 Cals. 



A 




II 




. . 4408 


B, 


V 


. . . 4317 Cals. 


| 4357 


B, 


a 


VI ... . 


. . . 4398 " 


M, 


n 
U 


XX. .. 




. . 4452 


TT, 


I 




. . 4371 


v, 
v, 


F 

G 


4355 Cals. 
. .. 4495 " 


i 4427 


VI, 


a 


H 


. . . 4534 " 


I 4535 


VI, 


u 


H 


. .. 4601 " 


VI, 


a 


J 


4502 " 



Average of 7 kinds 4437 " 

Oat straw, Ox F. . . . 4443 Cals. 

" OxG 4584 " 



Average 4513 " 

Wheat straw, Ox H 4553 Cals. 

Ox J 4387 " 



Average 



4470 



The digestible matter of the straw has apparently about the same 
heat value as that of hay. 

Metabolizable Energy. 

Protein. — A portion of the gross energy of the digested protein 
is removed in the urea and other nitrogenous products of metabo- 
lism, and in addition to this there is to be considered the possibility 
of a loss of energy by fermentation in the digestive tract. 

Losses in Methane. — In nine of the Mockern experiments in 
which wheat gluten or flesh-meal was added to the basal ration, the 
amount of carbon excreted in the form of hydrocarbons per day 
and head was as tabulated on the opposite page. 

The differences between the excretion with and without gluten 
are small in amount and are sometimes positive and sometimes 
negative, the averages being probably within the limit of experi- 
mental error. The percentage losses of energy in methane as 



THE bOOD AS A SOURCE OF ENERGY. 



3 11 





Period. 


Gluten 
Added, 
Grms. 


Carbon in 


Form of Hydrocarbons. 




From Basal 
Ration, 
Grms. 


With 

Addition of 

Gluten, 

Grms. 


Differences, 
Grms. 


Kuhn : 

Ox III 


3 
4 
3 

2a 
26 

1 
3 
3 
4 


680 
1360 

680 
1000* 
1000* 

1700 
1700 
1700 
1600 


186.4 
186.4 
187.7 
148.7 
148.7 


205.7 
207.6 
187.6 
162.9 
157.4 


+ 19.3 


" III 


+ 21.2 


" IV 


- 0.1 


" XX 


+ 14.2 


" XX 


+ 8.7 






Kellner : 

Ox B 


171.6 

208.9 
208.9 
183.0 
166.1 


184.2 

211.0 
200.9 
167.1 
170.7 


+ 12.6 
+ 2.1 


" B 


- 8.0 


" C 


-15.9 


" D 


+ 4.6 








191.7 


187.4 


- 4.3 



* Flesh-meal. 

computed in Table V of the Appendix, like the figures just given 
for the carbon of the methane, lead to the conclusion that the pro- 
tein of the food does not participate in the methane fermentation. 
Those figures were : 

Ox III, Period 3 10.81 per cent. 

" III, " 4 5.08 " " 

" IV, " 3 -1.26 " " 

" B, " 1 0.08 " " 

" B, " 3 -1.62 " " 

" C, " 3 -3.69 " " 

" D, " 4 1.91 " " 

Average -0.83 " " 

Kellner * reaches the same conclusion by comparing the ratio 
of the methane carbon to the amount of digested carbohydrates 
(nitrogen-free extract + crude fiber) in the several periods. The 
former amounted to the following per cent, of the latter in his 
experiments : 

*Loc. cit., 53, 420. 



312 



PRINCIPLES OF ANIMAL NUTRITION. 





Basal Ration, 
Per Cent. 


Basal Ration 
+ Gluten, 
Per Cent. 


Ox B 


2.94 
2.94 
2.71 
2.75 

2.87 

2.84 


2.96 
2.82 
2.41 
2.71 
3.19 

2.82 


" B 


" C 

" D 

" E 

Average 





Had the large quantities of digestible protein added to the basal 
rations produced any material amount of methane, that fact must 
have been reflected in the above percentages. This method of 
comparison takes into account the probable effect of the carbo- 
hydrates of the wheat gluten in increasing the production of 
methane, and the substantial agreement of the results with and 
without protein leads to the same conclusion as the preceding 
data. It seems fair to presume that this conclusion applies to 
protein in general, although a strict demonstration of it, especially 
for coarse fodders, would have its difficulties. 

Losses in Urine. — While the assumption that the urine is 
essentially an aqueous solution of urea leads to grave errors in the 
case of the carnivora, this is still more emphatically true of the urine 
of herbivora, particularly of ruminants. The presence in the urine 
of herbivora of hippuric acid and other nitrogenous compounds less 
highly oxidized than urea has of course long been known, while, 
as stated on p. 27, the presence of considerable amounts of non- 
nitrogenous organic matter was subsequently demonstrated by 
Henneberg and by G. Kiihn in the urine of ruminants. 

It follows from these facts that the energy content of the urine 
of these animals must be higher in proportion to its nitrogen than 
is the case with carnivora or with man, but the experimental dem- 
onstration of this fact and the realization of the extent and im- 
portance of the difference are of comparatively recent date. 

Cattle. — It is to Kellner * that we owe the first direct determi- 
nations of the potential energy of the urine of cattle. The two 
animals used in the experiment were fed, the one (A) on meadow 
hay, and the other (B) on meadow hay and oat straw. The results 
as regards the urine were as follows, per day and head: 

* hoc. cit., 47, 275. 



THE FOOD AS A SOURCE OF ENERGY. 



313 



Total nitrogen 

" carbon . 

Hippuric acid 

Total energy . 



Ox A. 



61 .28 grams. 
203.20 
145.00 " 
1945.00 Cals 



OxB 



46.63 grams 
161.30 " 
126.40 " 
1549.40 Cals. 



Assuming all the nitrogen not contained in the hippuric acid to 
have been in the form of urea, we have the following as the distri- 
bution of the carbon and of the energy of the urine : 





Ox A. 


OxB. 




Amount. 


Per Cent. 


Amount. 


Per Cent 


Carbon : 

In hippuric acid 

" urea 


Grms. 
87.48 
21.40 
94.32 


43.05 
10.53 
46.42 


Grms 
76.26 
15.75 
69.29 


47.28 

9.76 

42.96 


Total 

Energy • 

In hippuric acid 

" urea 

" other compounds. . . . 


203.20 

CaJs. 
821.30 
271.40 
852.30 


100.00 

42.23 
13.95 
43.82 


161.30 

Cals. 

715.90 
199.60 
633.90 


100.00 

46.20 
12.88 
40.92 


Total 


1945.00 


100.00 


1549.40 


100.00 







While the assumption that all the nitrogen was present either 
as hippuric acid or urea is not strictly correct, still the figures suffice 
to show, first, that a considerable proportion of the energy of the 
proteids of the food may be removed in the hippuric acid, and 
second, that the urine contains relatively considerable amounts of 
non-nitrogenous organic matter. Had the energy of the urine 
been computed from its nitrogen reckoned simply as urea the 
results would have been as follows : 





Ox A. 


Ox B. 


Calculated from N as urea 


331.6 Cals 
1945.0 " 


252.3 Cals 
1549 4 " 







In experiments by the writer on the maintenance ration of 
cattle,* determinations of the total energy of the urine of steers 
* Penna. Experiment Station, Bull 42, p. 150. 



314 



PRINCIPLES OF ANIMAL NUTRITION. 



were likewise made. Calculated per gram of nitrogen the results 
were as follows: 



Feed. 


Steer No. 1. 


Steer No. 2. 


Steer No. 3. 


Timothy hay and corn meal 


37. 79 Cals. 
40.64 " 
19.29 " 
25.02 " 
11.24 " 


28.35 Cals. 
34.25 " 
18.01 " 

10.77 " 




Cotton-seed feed -. 


28 82 Cals. 


Timothy hay 


12 47 " 


and starch 

Wheat straw, corn meal, and linseed meal 


10.95 " 



The methods employed to prepare the urine for combustion 
were not altogether satisfactory, and the range of possible error 
is rather large. In but two cases, however, was the energy of the 
urine less than twice that corresponding to its nitrogen calculated 
as urea (5.434 Cals.), while in one case it reached over seven times 
that amount. Neither carbon nor hippuric acid having been deter- 
mined, no computations can be made as to the amount of non- 
nitrogenous matter present. 

Jordan * has reached similar results on the urine of cows, the 
average energy content per gram of nitrogen being as follows: 





Total Nitrogen, 
Grms. 


Potential Energy, 
Cals. 


Energy per Grm. 
Nitrogen, Cals. 


Cow No. 12: 

Period 1 


87.0 

78.8 
42.8 
65.5 


1658.3 
1547.2 
1323.5 
1452.5 


19 06 


" 2 

" 3 

Cow No. 10 


19.63 
30,93 
22.18 



As in the writer's experiments, the energy per gram of nitrogen 
varies within wide limits, being greatest when the total nitrogen 
of the urine is least. In other words, it would appear that the 
non-nitrogenous ingredients of the urine of cattle are subject to 
less fluctuation than the nitrogenous ingredients. 

Kellner's later experiments have fully confirmed his earlier 
results, as will appear in greater detail in subsequent paragraphs. 
He finds that the carbon rather than the nitrogen of the urine is 
the measure of its potential energy, and that an estimate of 10 
Cals. per gram of carbon gave for his experiments results closely 
approximating the truth. f 

* New York State Experiment Station, Bull. 197, p. 28. 
f hoc. cit., 53, 437. 



THE FOOD AS A SOURCE OF ENERGY. 315 

Other Species. — We may probably assume without serious error 
that the results obtained with cattle apply in general to sheep and 
other ruminants. No direct determinations of the energy of the 
urine of the horse or the hog have yet been reported, but Zuntz & 
Hagemann * have made some estimates of it in the case of the 
horse on a mixed ration of hay, oats, and straw. They determined 
the total carbon and total nitrogen of the urine and, on the assump- 
tion that only urea and hippuric acid are present, compute the 
proportion of each of these, and thence the energy of the urine. 
They thus find the potential energy of the latter, per gram of nitro- 
gen, equal to 15.521 Cals. Neither hippuric acid nor energy having 
been determined directly, it is impossible to check the above com- 
putation or to ascertain whether any non-nitrogenous organic 
matter was present. It is to be noted, however, that the ratio of 
carbon to nitrogen in the urine was much lower than in Refiner's 
experiments on cattle, viz.: 

Zuntz & Hagemann 1.526 : 1 

Kellner, Ox A 3.315 : 1 

Ox B 3.458 : 1 

This fact clearly indicates that at least there was very much less 
non-nitrogenous matter present in the former case. 

Meissl, Strohmer & Lorenz f in their respiration experiments 
on swine likewise determined carbon and nitrogen in the urine. 
Computed by the method of Zuntz & Hagemann the energy of the 
urine averaged 9.55 Cals. per gram of nitrogen, while the average 
ratio of carbon to nitrogen was 0.745 : 1. These results would 
seem to indicate that the loss of energy in the urine of the hog 
is not very much greater than in that of the carnivora. 

Metabolizable Energy of Protein of Concentrated Feeds. 
— Accepting it as demonstrated that there is no material loss of 
potential energy in the form of fermentation products of protein, 
the data regarding the energy of the urine just considered afford 
the basis for an approximate estimate of the metabolizable energy 
of the digested protein. 

Cattle. — Refiner's experiments upon cattle afford data for com- 
puting the metabolizable energy of the digested protein of wheat 

* Landw. Jahrb., 27, Supp. Ill, 239. f Zeit. f. Biol, 22, 63. 



316 



PRINCIPLES OF ANIMAL NUTRITION. 



gluten and of beet molasses. The method of computation is pre- 
cisely similar to that already employed for calculating the metabo- 
lizable energy of the total organic matter; that is, the results upon 
the basal ration are subtracted from those upon the ration con- 
taining the material under experiment. 

Taking as an example the results upon wheat gluten with Ox C 
in Periods 1 and 3 we have the following comparison : 





Digested. 


Energy 

of Urine, 

Cals. 


Gain of 
Nitrogen 

by 

Animal, 

Grms. 




Protein, 
Grms. 


Crude 
Fiber, 
Grms. 


Nitrogen- 
Free 
Extract, 
Grms. 


Ether 

Extract. 
Grms. 


Period 3 


1694 
598 


1279 
1289 


5648 
5464 


34 
40 


2592 . 8 
1666.4 


20.31 


" 1 


16.01 


Difference 


1096 


-10 


184 


-6 


926.4 


4.30 



The difference of 4.3 grams in the amount of nitrogen gained 
by the animal is equivalent to 32 Cals. which would otherwise have 
appeared in the urine. This added to the 926.4 Cals. actually 
found makes a total of 958.4 Cals. for the increase in the potential 
energy of the urine clue to the 1096 grams of protein digested. 
There are also differences in the amount of non-nitrogenous matters 
digested, particularly of the nitrogen-free extract. As Tables I, III 
and IV of the Appendix show, both starch and crude fiber, as repre- 
sented by the extracted straw, tend to diminish the amount of energy 
carried off in the urine. These differences were observed when from 
2 to 2.5 kilograms of these substances were added to the basal 
ration. If the differences are proportional to the amount fed, the 
energy corresponding to the small difference observed in this ex- 
periment would not exceed 15 or 20 Cals., and may be neglected, 
while the maximum difference in any experiment of the series 
would probably not exceed 70 to 75 Cals. Assuming that all the 
additional protein digested came from the wheat gluten, we have 
for the corresponding energy of the urine 

958 . 4 -^ 1096 = . 874 Cals. per gram protein digested. 

Subtracting this from the total energy of the digested protein as 
found on p. 309, viz., 5.975 Cals., we have 5.101 Cals. as the metabo- 



THE FOOD AS A SOURCE OF ENERGY. 



3 J 7 



lizable energy of one gram of digested protein of wheat gluten in 
this experiment. 

For the four experiments upon this substance, computed as in 
the above example, the results were as follows: 



Protein 
digested 

from 
Gluten, 
Grms. 



Difference in 
Energy of Urine.* 



Total, 
Cals. 



Per Grm. of 

Protein, 

Cals. 



Ox B, Periods 1 and 3 

" C, Period 3 

" D, " 4 

" E, " 4 

Average 



2185 
1096 
1056 
1148 



2547.3 

958.4 

1061.1 

1362.1 



1.166 
0.874 
1.005 
1.186 



1371 



1482.2 



1.081 



* Corrected to nitrogen equilibrium. 

Subtracting from the total energy of the digested protein the 
potential energy carried off in the urine we have for the metab- 
olizable energy of one gram of protein 

5 . 975 Cals. - 1 . 081 Cals. = 4 . 894 Cals. 

If we use Ritthausen's factor, 5.7, for proteids, the average 
digested protein becomes 1250 grams and the loss of energy in the 
urine 1.190 Cals. per gram of protein. Subtracting this from 6.148 
Cals., the gross energy of one gram of NX5.7 (p. 309), we have for 
the metabolizable energy of the latter 4.958 Cals. per gram. 

The average increase in the energy of the urine for each addi- 
tional gram of nitrogen excreted in these experiments (6.756 Cals.) 
was almost exactly the same as Rubner found in his experiment 
on extracted lean meat (6.695 Cals.). This may be taken as indi- 
cating that the process of proteid metabolism is substantially the 
same in both classes of animals, while the fact that the result is 
notably greater than the energy of urea shows that in the herbivora 
as in the carnivora other waste products than urea result from the 
proteid metabolism. 

In three other experiments beet molasses was added to the 
basal ration, resulting in the digestion of an increased amount of 
nitrogenous matter. Computing the results as in the case of the 



3*8 



PRINCIPLES OF ANIMAL NUTRITION. 



wheat gluten, and assuming that the large amounts of soluble 
carbohydrates digested had no effect on the potential energy of the 
urine, the results were as follows : 





Protein Digested 

from Molasses, 

Grms. 


Difference in Energy of Urine.* 




Total, Cals. 


Per Grm. Protiein, 
Cals. 


OxF 

" H 

" J 


117 
160 
122 


256.1 
240.3 
192.6 


2.189 
1.502 
1.579 


Average 


133 


229.7 


1.727 



* Corrected to nitrogen equilibrium. 

It will be seen that the loss of energy in the urine is much 
greater than in the case of the gluten or than in Rubner's experi- 
ments with carnivora. Since it is improbable that the soluble 
carbohydrates of the molasses escape oxidation, it would appear 
that some of the nitrogenous material of the latter must have 
passed through the system unmetabolized. Kellner suspects that 
it is made up in part at least of xanthin bases. 

If we consider the nitrogen of the molasses to represent crude 
protein (NX6.25) with a heat value of 5.711 Cals. per gram, the 
metabolizable energy per gram would be 3.984 Cals. In view, 
however, of the fact that only a very small proportion of the nitro- 
gen of the molasses is in the proteid form, such a calculation seems 
of doubtful value. 

Swine. — In the investigations of Meissl, Strohmer and Lorenz* 
upon the production of fat from carbohydrates (p. 176) the carbon 
and nitrogen of the urine were determined in six experiments. 

Applying to the results Zuntz & Hagemann's method of 
computation (p. 315) we obtain the following estimates for the 
energy per gram of nitrogen in the urine of the hog in these 
experiments and for the corresponding metabolizable energy of the 
digested protein: 



* Zeit. f. Biol., 22, 63. 



THE FOOD AS A SOURCE OF ENERGY. 



319 



Experi- 
ment 
No. 



Feed. 



Rice 

Barley 

Whey, rice, and flesh meal 
Nothing 



Nitrogen 

as Urea, 

Grms. 



9.58 
9.22 
13.04 
59.89 
9.35 
6.48 



Nitrogen 

as Hip- 

puric 

Acid, 

Grms. 



0.88 
1.04 
1.04 
1.17 
0.45 
0.29 



Total 
Energy 
of Urine, 

Cals. 



115.7 
125.6 
146.5 
410.0 

83.7 
56.4 



Energy 
per Grm. 

of 

Nitrogen, 

Cals. 



11.06 

12.24 

10.40 

6.72 

8.54 

8.33 



Metabo- 
lizable 
Energy 

per 

Grm. 

Protein, 

Cals. 



3.941 
3.753 
4.048 
4.636 
4.344 
4.379 



Kornauth & Arche * report the following results on the urine of 
swine fed chiefly upon cockle: 



Experiment 
No. 


Nitrogen, 
Grms. 


Carbon, 
Grms. 


Ratio, 
C :N. 


1 

2 

3 

Average 


10.56 
10.30 
10.41 


10.30 
9.53 
9.96 


0.975 : 1 
0.926 : 1 
0.957 • 1 


10.42 


9.93 


0.953 : 1 



The results, computed as in the previous case, make the average 
energy content of the urine 10.27 Cals. per gram of nitrogen, 
equivalent to a metabolizable energy of 4.067 Cals. per gram of 
protein. 

In the two fasting experiments of Meissl, Strohmer & Lorenz 
the ratios of carbon to nitrogen and of computed energy to nitro- 
gen are similar to those obtained with fasting carnivora. The 
abundant supply of proteids in the diet in the fourth experiment 
seems to have had the effect of reducing these ratios to values 
comparable with those obtained by Rubner for extracted meat 
and by Kellner for the digested protein of wheat gluten. These 
facts seem to indicate clearly that the nature of the proteid meta- 
bolism in all these animals is substantially the same. In the ex- 
periments in which ordinary grains were used, the computed energy 
content of the urine is notably greater relatively to its nitrogen. 
How far the excess of carbon found in these cases was due to an 



* Landw. Vers. Stat., 40, 177. 



320 PRINCIPLES OF ANIMAL NUTRITION. 

increased formation of hippuric acid and what part of it, if any, is 
to be ascribed to the presence of non-nitrogenous matter in the 
urine, the experiments afford no means of estimating. 

The Horse. — Zuntz & Hagemann's results on the horse, p. 315, 
although the result of feeding mixed rations, may be conveniently 
considered here. The computed energy of the urine was 15.521 
Cals. per gram of nitrogen, equivalent to 2.483 Cals. per gram of 
protein. Assuming for the latter, as before, a value of 5.711 Cals., 
there remains for the metabolizable energy 3.228 Cals. per gram. 

Protein of Coarse Fodders. — Almost the only data on this 
point are those afforded by Kellner's experiments upon cattle. In 
those in which coarse fodders were used alone we can of course 
compute the metabolizable energy of the protein directly from the 
amount digested and from the energy of the urine. In those 
experiments in which coarse fodders were added to a basal ration 
we can compare the two experiments in the same manner as those 
upon gluten, neglecting, as in that case, the differences in the non- 
nitrogenous nutrients digested. 

Passing over the details of the computation, the final results, 
including the metabolizable energy of the digested protein com- 
puted upon the assumption that its gross energy equals 5.711 
Cals. per gram, are as given in the table on the opposite page.* 

The writer's experiments on timothy hay, the results of which 
as regards the energy of the urine have already been given on p. 314, 
when computed in the same manner as the above experiments give 
the following results for the metabolizable energy of the digested 
protein : 

Steer 1 2.625 Cals. 

" 2 2.830 " 

" 3 3.716 " 

Average 3.057 " 

Influence of Non-nitrogenous Matter of Urine. — In the previous 
paragraphs there appeared reasons for supposing that the processes 
of proteid metabolism are essentially the same in all domestic 

* The figures given in this table for digested protein, energy, etc., refer 
solely to that derived from the coarse fodder and not to that of the total 
ration. 



THE FOOD AS A SOURCE OF ENERGY. 



321 



Protein 

(NX6.25) 

Digested, 

Grms. 



Difference in 
Energy of Urine.* 



Total, 
Cals. 



Per Grm. of 

Protein 

Digested, 

Cals. 



Metaboliz- 

able Energy 

per Grm. 

Digestible 

Protein, 

Cals. 



Meadow Hay 
No. I, Ox 
" II, " 
" V, " 
" V, " 
" VI, " 
it vi, " 
" VI, « 
" A, " 
" B, " 
» B, " 
" M, 



A 

I 

F 

G 

H, Period 1 . 
H, " 7. 

J 

II 

V 

VI 

XX 



Average 



Oat Straw : 
No. II, Ox F. 
" II, " G. 

Average . . . 



Wheat Straw : 
No. I, Ox H. 
" I, " J. 

Average . . 



440 
342 
137 
146 
193 
220 
213 
413 
451 
458 
540 



323 



35 

48 



42 



-11 
14 



1991.3 

1686.9 

583.2 

556.5 

781.4 

798.0 

930.5 

1925.7 

1559.3 

1737.9 

3224 . 6 



526 
933 
257 
812 
049 
632 
368 



4.662 
3.456 
3.794 
5.973 



1434 . 1 



354.2 
274.0 



4.439 



10.120 
5.710 



314.1 



289.7 
413.2 



7.478 



(?) 
29.520 



351.5 



(?) 



1.185 
0.778 
1.454 
1.899 
1.662 
2.079 
1.343 
1.049 
2.255 
1.917 
-0.262 



1.272 



-4.409 
-0.001 



-1.767 



(?) 
-23.809 



(?) 



* Corrected to nitrogen equilibrium. 



animals and consequently that the metabolizable energy of the 
proteids cannot be widely different. In these results upon coarse 
fodders we meet an apparent contradiction of this conclusion, the 
metabolizable energy of the digestible protein as above computed 
being quite variable and much lower than the values found for pure 
proteids, while in the straw we get large negative values. 

These latter results, however, while appearing at first sight para- 
doxical, furnish the clue to the apparent contradiction. In the 
case of the straws it is evident that a very considerable part of the 
potential energy of the urine must have been contained in non- 
nitrogenous substances, and that the latter must have been derived 
largely from the non-nitrogenous matter of the food. We have 
already seen, however, that these non-nitrogenous excretory prod- 



322 PRINCIPLES OF ANIMAL NUTRITION. 

ucts are a normal constituent of the urine of cattle both on hay and 
on mixed rations. Their effect on the computation becomes more 
obvious in the case of the straws, simply because of the relatively 
small amount of protein in the latter feeding-stuffs. In these cases 
we get impossible results when we assume that all the potential 
energy of the urine is derived from the proteids metabolized, but it 
is clear that the results on the hays must be affected by the same 
error, and there is little question that the low and variable results 
noted in the table are to be explained in part in this way. We 
know no essential difference between the real proteids of the differ- 
ent coarse fodders, nor between those of coarse fodders and grain, 
nor any reason why they should not be metabolized in substantially 
the same way in the body and possess approximately the same 
metabolizable energy. It would seem more reasonable, then, to 
assume that the proteids of coarse fodders are metabolized sub- 
stantially like those of concentrated fodders, and to take provision- 
ally the results obtained for the protein of wheat gluten as repre- 
senting approximately the metabolizable energy of the digested 
protein of the total ration, while we regard the remaining energy 
of the urine as derived largely from the non-nitrogenous nutrients 
of the food. 

Hippuric Acid. — The statement last made, however, requires 
some modification. Not a little of the potential energy of the urine 
of cattle is contained in the hippuric acid which these animals 
excrete so abundantly. This being a nitrogenous product, it is 
natural to look upon it as derived from the proteids of the food, 
but it must not be forgotten that this is only partially true. Its 
glycocol portion originates in the proteids, but its phenyl radicle 
appears to be derived in these animals largely, if not wholly, from 
the non-nitrogenous ingredients of the food (compare p. 45). If 
the metabolism of one gram of protein is arrested at the glycocol 
stage by the presence in the organism of benzoic acid, there has 
already been liberated from it about 3 Cals. of energy, while about 2.7 
Cals. remain in the glycocol. The resulting hippuric acid, however, 
contains about 11.6 Cals. of potential energy, or more than the 
original protein. In this case, then, the larger share of the energy 
of the excretory product (8.9 Cals. out of 11.6 Cals.), although con- 
tained in a nitrogenous substance, is derived ultimately from the 



THE FOOD AS A SOURCE OF ENERGY. 3 2 3 

non-nitrogenous matter of the food. It is clear, then, that the 
non-nitrogenous moiety of the hippuric acid and the non-nitrogen- 
ous organic matter of the urine together represent a large share 
of the potential energy of the latter, and that it is quite as in- 
correct to compute the metabolizable energy of the protein on the 
assumption that all the energy of the urine is derived from it as it 
is, on the other hand, to simply deduct from its gross energy the 
energy of the equivalent amount of urea. 

Ether Extract. — Our only data upon this ingredient are fur- 
nished by the four experiments upon steers by Kellner in which 
peanut oil was added to the ration. In the first two experiments 
this oil was emulsified by means of a small quantity of soap made 
from the same oil. The result was a milky fluid which was readily 
digestible and which caused no considerable decrease in the digesti- 
bility of the basal ration. In the second two experiments the oil 
was emulsified with lime-water, giving a thickish mass which was 
not very well digested and which, in the case of Ox F particularly, 
caused a considerable decrease in the digestibility of the crude fiber 
and nitrogen-free extract of the basal ration. It should be noted 
that in the experiment with Ox E the oil was not added to a basal 
ration, but was substituted for a part of the bran. From Table VI 
of the Appendix we obtain the summary tabulated on the next 
page, showing the effects of the oil upon the loss of energy in the 
gaseous hydrocarbons and in the urine, the results of the experi- 
ment on Ox E being included. 

Upon the evidence of these four experiments, bearing in mind 
that the one with Ox E was upon the substitution of oil for bran, 
we should not be inclined to ascribe to the fat of the food any con- 
siderable effect either upon the formation of hydrocarbons or upon 
the amount of potential energy carried off in the urine. As regards 
the hydrocarbons, the differences in the cases of Oxen D and G are 
insignificant. In the case of Ox F, on the contrary, the production 
of hydrocarbons was reduced nearly one half; this it may be noted 
was the case in which there was a considerable effect upon the 
digestibility of the basal ration. As regards the energy of the urine, 
the differences, except in the case of Ox E, are relatively small and 
are in both directions. 

Provisionally, therefore, we are probably justified in assuming 



3 2 4 



PRINCIPLES OF ANIMAL NUTRITION. 



Ani- 
mal. 


Period. 


Energy of Urine 
(Corrected). Cals. 


Energy of 
Methane, Cals. 


D 


3 
1 

3 
1 

5 
3 

5 
3 


With oil 


2851.2 
2407 . 


2909 . 


D 


Basal ration 


2957 . 




Differences 






-55.8 

2026 . 2 
2312.9 


-48.0 


E 


With oil 


2640.8 


E 


Basal ration 


2950.4 




Differences 






-286.7 

1455.0 
1530.0 


-309.6 


F 


With oil 


1369.1 


F 


Basal ration 


2560.7 




Differences 

With oil 

Basal ration 

Differences 




G 
G 


-75.0 

1452.1 
1359 . 6 


-1191.6 

2371.2 

2524.7 




92.5 


-153.5 









as Kellner does that none of the energy of the fat was lost either in 
the hydrocarbons or in the urine, and that consequently the metab- 
olizable energy of the digested fat was the same as its gross energy, 
namely, 8.821 Cals. per gram, as given on p. 308. If we assume that 
the ether extract of hay behaves like the peanut oil, taking no part 
either in the production of methane or in the loss of energy through 
the urine, its metabolizable energy would likewise be the same as 
its gross energy, namely, 8.322 Cals. per gram, as computed on p. 305. 
No results upon the metabolizable energy of the ether extract are 
available in the case of other species of herbivorous animals. 

Carbohydrates. — Those of Kellner's experiments in which 
starch,, as a representative of the readily digestible carbohydrates. 
and extracted straw, consisting largely of " crude fiber," were added 
to the basal ration afford data for an approximate computation of 
the metabolizable energy of this group of nutrients in the ox, and 
experiments by Lehmann, Hagemann & Zuntz afford partial data 
for the horse. 

Starch. — The results of the Mockern experiments, as recorded 
in Tables III and IV of the Appendix, show that the starch had 
but a slight effect upon the amount of potential energy carried off 
in the urine of the ox, although the general tendency was to 



THE FOOD AS A SOURCE OF ENERGY. 



3 2 5 



diminish it slightly. On the other hand, the formation of hydro- 
carbons was markedly increased except in two cases. It has al- 
ready been shown that the proteids of the food do not take part in 
the production of these gases, and that the same is probably true 
of the fat under normal conditions. Neglecting the small effects 
upon the urine, therefore, we may compare directly the increase in 
the digested carbohydrates with the increase in the gaseous hydro- 
carbons, using for this purpose the differences between the two 
rations uncorrected for the slight variations in the consumption of 
dry matter. 

Taking first the last five of Refiner's experiments.* which seem 
to represent the most normal conditions, we have the following : 





Difference in Carbohydrates 
Digested. 


Difference in 




Crude Fiber, 
Grms. 


Nitrogen-free 

Extract, 

Grms. 


Methane, 
Cals. 


Ox D, Period 2 

" F " 4 

" G " 4 

" H, " 3 

"J " 3 


-64 
-64 
-50 
-26 
- 9 


+ 1388 
+ 1609 
+ 1598 
+ 1861 
+ 1501 


+ 424.4 
+ 822.0 
+ 645.8 
+ 604.5 
+ 769.9 


Totals 


-213 


+ 7957 


3266.6 







Assuming that the same proportion of hydrocarbons is pro- 
duced in the fermentation of crude fiber as in that of starch, we 
may compare the algebraic sum of the two with the energy of the 
methane as follows: 

3266 . 6 Cals. +■ (7957 - 213) = . 422 Cals. per gram. 
Subtracting the latter result from the gross energy of the digested 
nitrogen-free extract of starch, we have for the metabolizable 
energy of the latter 

4 . 185 Cals. - . 422 Cals. = 3 . 763 Cals. per gram. 

In the experiments on Oxen B and C the basal ration was a 
heavy one, with a rather wide nutritive ratio, and already con- 
tained large amounts of digestible carbohydrates. Under these cir- 
cumstances the added starch was very imperfectly digested, while 
*Loc. cit., 53. 422. 



326 



PRINCIPLES OF ANIMAL NUTRITION. 



the production of hydrocarbons was diminished. Kellner suggests 
that the latter effect may have been due to a partial suppression 
of the organisms causing the methane fermentation by other species, 
and suspects that the presence of large amounts of carbohydrates 
along with little protein favors this result. At any rate, the con- 
ditions are evidently unusual if not abnormal. 

In Kuhn's experiments the starch was added to a ration of 
coarse fodder. The nutritive ratio was wide, but the absolute 
amount of carbohydrates was much less than in the two experiments 
by Kellner just mentioned, less starch appeared to escape diges- 
tion, and the production of hydrocarbons was increased in every 
case. The following are Kuhn's* results: 



Difference in Carbohydrates 
Digested. 



Crude Fiber, 
Grms. 



Nitrogen-free 
Extract, Grms. 



Difference in 

Energy of 

Methane, 

Cals. 



IV, ' 


2 


V, ' 


2a 


V, ' 


26 


V, ' 


3 


VI, 


2a 


VI, ' 


26 


VI, ' 


3 


Totals . . 





-220 
-180 
-195 
-130 
-176 
-146 
- 88 
-156 



1529 
1408 
1537 
1539 
2619 
1468 
1554 
2587 



706.2 
856.7 
752.6 
665.5 

1181.0 
729.5 
649.9 

1407.0 



-1291 



14241 



6948.4 



Assuming as before the equivalence of crude fiber and nitrogen- 
free extract as regards the production of hydrocarbons we have 

6948. 4 Cals. -(14241 -1291) = 0.537 Cals. per gram, 
4 . 185 Cals. - . 537 Cals. = 3 . 648 Cals. per gram. 

Determinations by Lehmann, Hagemann & Zuntz f of the 
amount of methane produced by the horse will be considered in 
connection with the metabolizable energy of crude fiber. Zuntz J 
has pointed out that the fermentation of the food in the horse takes 
place largely in the ceecum and after the more digestible carbo- 
hydrates have been resorbed. Accordingly he regards the metabo- 

* hoc. tit., 44, 570. 

f Landw. Jahrb., 23, 125. 

± Arch. ges. Physiol., 49, 477. 



THE FOOD AS A SOURCE OF ENERGY. 



3 2 7 



lizable energy of starch and similar bodies in this animal as equal 
to their gross energy, viz., 4.185 Cals. per gram in the case of 
starch. 

Extracted Straw. — The two experiments in which extracted 
straw was added to the basal ration, when computed as in the case 
of the starch experiments, give the following results: 





Difference in Carbohydrates 
Digested. 


Difference in 
Energy of 




Crude Fiber, 
Grms. 


Nitrogen-free 

Extract, 

Grms. 


Methane, 
Cals. 


Ox H, Period 5 


2046 
1987 


439 
449 


1425 . 1 


" J, " 5 


1425.2 






Totals 


4033 


888 


2850.3 







The loss of energy in the hydrocarbons equals 0.579 Cals. per 
gram of total digestible carbohydrates (of which 82 per cent, was 
crude fiber), and the corresponding metabolizable energy of the 
carbohydrates is 3.668 Cals. per gram. This is a materially lower 
figure than Kellner found for starch and indicates that the loss of 
energy in the gaseous products of fermentation is greater in tie 
case of crude fiber than in that of the more soluble carbohydrates, 
an indication which, as we shall see, is confirmed by the results of 
other experiments. 

Carbohydrates of Coarse Fodders. — Upon the same two 
assumptions, viz., that the carbohydrates are the sole source of the 
gaseous hydrocarbons, and that the latter represent the entire loss 
of energy from the digested carbohydrates, we may compute the 
metabolizable energy of the total digestible carbohydrates of the 
various coarse fodders exactly as in the case of the extracted straw, 
the results being tabulated on the next page. 

If we average the results for. each feeding-stuff and compute 
them as in the foregoing cases, our findings are as given on p. 329, 
where the rations are arranged in the order of their crude fiber 
content. In computing the metabolizable energy, the gross energy 
of the digested carbohydrates has been assumed to be the average 



328 



PRINCIPLES OF ANIMAL NUTRITION. 
COARSE FODDERS ALONE. 







Digested Carbohydrates. 










Energy of 


Animal. 




Crude Fiber, 
Grms. 


Nitrogen- 
free 
Extract, 
Grms. 


Methane, 

Grms. 


A 


Meadow hay I 


1262 


2713 


2113.7 


II 


" " A 


1765 
1572 


2610 
2315 


3137.2 


V 


" B 


2268 . 5 


VI 


" B 


1642 


2420 


2480 . 6 


XX 


" M 


1560 


2999 


2646 . 1 


I 


" II 


1266 


2348 


2092 . 3 


B 


" and oat straw. . 


1702 


2357 


2331.2 


III 


Clover " " " " 


1676 


2226 


2670 . 1 


IV 


11 11 11 it u 


1565 


2145 


2491.3 



COARSE FODDER ADDED TO BASAL RATION. 





Period. 




Difference in 
Carbohydrates Digested. 


Energy of 

Methane, 

Cals. 


Animal. 


Crude Fiber, 
Grms. 


Nitrogen- 
free 
Extract, 
Grms. 


F 

G 

H 

H 

J 

F 

G 

H 

J 


1 

2 
2 
7 
2 
2 
1 
1 
1 


Meadow hay V 

" V 

" VI 

" VI 

" VI 

Oat straw II 

" II 

Wheat straw I 

U it T 


546 

538 
703 
739 
683 
694 
595 
821 
829 


836 

886 

1129 

1236 

1213 

721 

684 

524 

616 


689.9 
907.4 
727.2 
898.0 
984.8 
679.2 
923.4 
1213.0 
1281.0 



of the results given on pp. 304 and 306 for the digested crude fiber 
and nitrogen-free extract of coarse fodders, viz., 4.226 Cals. per 
gram. 

As a whole, the figures given on p. 329 show a tendency 
toward an increased production of methane with an increase in 
the proportion of crude fiber, but considerable variations are 
found in individual cases. It is evident, therefore, from these 
results, as well as from those already cited in connection with the 
experiments upon starch and upon molasses, that a variety of 
factors influence the extent of this fermentation. 



THE FOOD AS A SOURCE OF ENERGY. 



329 





100 Parts Digested 

Carbohydrates 

Contain 


Energy of 
Methane 
per Grm. 
Digested 
Carbo- 
hydrates, 
Cals. 


Metaboliz- 
able Energy 
of Total 
Digested 
Carbo- 
hydrates 
per Grm., 
Cals. 




Crude 
Fiber. 


Nitrogen- 
free 
Extract. 


Meadow hay I 

" M 


31.7 
34.2 
35.0 
37.3 
38.6 
40.4 
41.9 
42.6 
47.8 
59.1 


68.3 
65.8 
65.0 
62.7 
61.4 
59.6 
58.1 
57.4 
52.2 
40.9 


0.532 
0.580 
0.579 
0.458 
0.569 
0.597 
0.574 
0.678 
0.595 
0.894 


3.694 
3.646 


" II 


3.647 


" VI 

" V 

" B 

" " and oat straw 


3.768 
3.629 
3.657 
3.652 


Clover " " " " 

Oat straw II 


3.548 
3.631 


Wheat straw V 


3.332 







A comparison of the methane production with the digestibility 
of the feeding-stuffs shows in general that the former is greatest 
when the latter is least, that is, with the feeding-stuffs which tend 
to remain longest in the digestive tract. Here too, however, excep- 
tions occur, and it would appear that the physical condition of the 
feeding-stuff is not without its influence. The exceedingly com- 
plicated nature of digestion in ruminants, and the fact that it is a 
chemical rather than a physiological process, and is therefore sub- 
ject to considerable variations according to the nature and amount 
of the food, render it difficult, if not impossible, with our present 
knowledge to compute very trustworthy averages for the amount 
of energy carried off in this way. 

Crude Fiber. Ruminants. — Both the ultimate composition and 
the heat of combustion of the digested nitrogen-free extract have 
been shown to agree quite closely with those of starch, and the 
nutritive value of the former has commonly been assumed to be 
the same as that of the latter. If we are justified in somewhat 
extending this, and assuming that the nitrogen-free extract of 
coarse fodders suffers the same loss by the methane fermentation 
as does starch, the figures of the preceding paragraphs supply 
data for computing the corresponding loss suffered by the 
crude fiber. 



33° 



PRINCIPLES OF ANIMAL NUTRITION. 



In the case of the extracted straw, for example, there was 
digested in the total of the two experiments : 

Crude fiber 4033 grams 

Nitrogen-free extract 888 " 

Assuming the loss of energy in the methane to have been 0.422 
Cal. per gram of nitrogen-free extract digested (the same as that 
found by Kellner for starch, p. 325), the 888 grams of these sub- 
stances correspond to a loss of 374.7 Cals. Subtracting this from 
the total loss of 2850.2 Cals., we have 2475.5 Cals. as the energy of 
the methane produced from 4033 grams of crude fiber, which is equal 
to 0.614 Cal. per gram. The total energy of the digested crude fiber 
was shown on p. 304 to be approximately 4.220 Cals. per gram. 
Subtracting the loss in the methane, 0.614 Cal., leaves 3.606 Cals. 
as the metabolizable energy of one gram of digested crude fiber. 
A similar computation of the average results upon the other coarse 
fodders affords the figures of the following table for the metabo- 
lizable energy of one gram of digestible crude fiber : 



Digestible Crude Fiber of 



Loss in Methane, 
Cals. 



Metabolizable 

Energy, 

Cals. 



Extracted straw 

Hay fed alone 

" added to basal ration 

Oat straw added to basal ration . . 
Wheat straw added to basal ration 



0.614 
0.909 
0.614 
0.783 
1.219 



3.606 
3.311 
3.606 
3 . 437 
3.001 



The loss of energy in methane, as thus computed, is in all 
instances greater than in the case of starch. Owing, however, to 
the slightly higher value obtained for the gross energy of the 
digested crude fiber, the difference in metabolizable energy between 
starch and crude fiber is somewhat less marked, and is hardly 
sufficient of itself to justify assigning a materially lower nutritive 
value to the latter. 

It is worthy of note also that the loss in the methane appears to 
be a very variable one, justifying the conclusion already reached 
that other factors than the proximate composition of the food ma- 
terially affect the extent of the methane fermentation. 

The Horse. — The production of methane by the horse appears 
to be much less copious than that by ruminants. Lehmann, Hage- 



THE FOOD AS A SOURCE OF ENERGY. 



33 1 



mann & Zuntz * in eight respiration experiments obtained the 
following results, the hydrocarbons being computed as methane: 



Crude Fiber Digested. 


Methane Excreted 


698 


5 grams 


26 . 8 grams 


538 


9 " 


33.4 " 


451 


7 " 


13.0 " 


it 


n 


20.0 " 


n 


a 


16.4 " 


a 


a 


31.0 " 


a 


a 


22.1 " 


tt 


tt 


23.0 " 



As already noted on p. 326, Zuntz f has pointed out that the 
fermentation of the food in the horse takes place largely in the 
coecum and after the more digestible carbohydrates have been 
resorbed. The authors consequently compute the excretion of 
methane entirely upon the crude fiber of the food. On the average 
of the eight somewhat discordant experiments, in which the food 
consisted of oats, hay, and cut straw, 100 grams of digested crude 
fiber yielded 4.7 grams of methane, which corresponds exactly with 
the results reported by Tappeiner \ for the artificial fermenta- 
tion of cellulose. In the same experiments an excretion of approxi- 
mately 0.203 gram of hydrogen per 100 grams digested crude fiber 
was observed. Deducting the corresponding amounts of energy 
from the energy of the apparently digested cellulose we have — 

Total energy of 1 gram 4 . 220 Cals. 

Energy of CH 4 (0.047 gram). 0.627 Cal. 

Energy of H (0.002 gram)... 0.070 " 0.697 Cal. 



Metabolizable energy of 1 gram 3 . 523 Cals.§ 

While less methane is apparently produced by the horse than 
by the ox, the assumption that it all arises from the fermentation 
of the crude fiber gives the latter a metabolizable energy not greatly 
different from that found in the case of the ox. It is of course 

* Landw. Jahrb., 23, 125. 
t Arch. ges. Physiol., 49, 477. 
% Zeit. f. Biol., 20, 88. 

§ As computed by the authors, 3.487 Cals. on the basis of 4.185 Cals. 
total energy per gram of crude fiber. 



332 



PRINCIPLES OF ANIMAL NUTRITION. 



implied in this that the metabolizable energy of the digested nitro- 
gen-free extract is the same as its gross energy. 

Summary. — The results recorded in the preceding paragraphs 
regarding the metabolizable energy of the several classes of digesti- 
ble nutrients are summarized in the following table : 

METABOLIZABLE ENERGY OF DIGESTIBLE NUTRIENTS. 





Cattle. 

Cals. per 

Grm. 


Horse, 

Cals. per 

Grm. 


Swine, 

Cals. per 

Grm. 


Protein (NX 6.25): 

From wheat gluten 


4.894 
4.958 
3.984 






" (NX5.7) 




" beet molasses 




" mixed grain 


4.0S3 


" ration of oats, hay, and straw 
" meadow hay 


1.272 
3.057(?) 

(?) 

8.821 
8.322 

3.763 
3.648 


3.228 

4.185 
3.523 




" timothy hay 




" straw 




Fat: 

From peanut oil 

" hay (ether extract) 

Carbohydrates : 

Starch, Kellner's experiments 

" Kilhn's 




Nitrogen-free extract (assumed) 




Crude fiber, of extracted straw 


3.606 
3.311 
3.606 
3 . 437 
3.001 




" " hay fed alone ... 




" added to basal ration . 
" " oat straw 




" " " wheat straw .... 




" " mixed ration 











Perhaps the most striking thing about these figures is the wide 
range of the results upon the same class of nutrients. For reasons 
already stated, this is most noticeable with the protein, but it is 
sufficiently marked also with the other two groups. Moreover, 
such meager data as we possess regarding other animals than the ox 
indicate that the results vary with the species of animal, a fact 
which should not surprise us, but which, nevertheless, adds mate- 
rially to the complexity of the subject and greatly widens the range 
of necessary investigation. It is obvious, therefore, that at present 
our knowledge is too imperfect to allow of the assignment of average 
values for the metabolizable energy of the different classes of 



THE FOOD AS A SOURCE OF ENERGY. 333 

nutrients (as ordinarily determined) even for a single species of 
animal. 

The results tabulated above, however, are amply sufficient to 
justify the statement on p. 279 that Rubner's averages are not appli- 
cable to herbivorous animals, and that the metabolizable energy 
as computed with their aid is likely to vary widely from the truth. 
Indeed, since Rubner's factor for fat (9.3 Cals. per gram) is 2.27 
times that for carbohydrates and protein (4.1 Cals. per gram) a 
computation of the metabolizable energy of feeding-stuffs or rations 
as it has not uncommonly been made simply gives a series of figures 
about 4.1 times as great as that obtained for total digestible matter 
when the digestible fat is reduced to its starch equivalent by multi- 
plication by 2£. So far, then, as a comparison of one feeding-stuff 
or ration with another is concerned, this process adds no whit to our 
knowledege. It does, it is true, give some idea, albeit an inade- 
quate one, of the total amount of metabolizable energy present. As 
yet, however, our accurate knowledge of the energy requirements of 
domestic animals for various purposes is comparatively meager. 
If we base our computations on the feeding standards now current, 
we simply repeat with them the useless multiplication performed 
on the feeding-stuffs. On the other hand, if we take the results of 
such exact experiments on the metabolism of energy as are available, 
then, as the above results show, we shall be computing the energy 
requirements upon one basis and the energy supply upon a mate- 
rially different one. 

Significance of the Results. — A much more fundamental prob- 
lem than that raised in the foregoing paragraph confronts us when 
we come to reflect upon the general method by which it has been 
attempted to compute the metabolizable energy of nutrients, and 
to consider the real significance of the results. In so doing we may 
properly confine ourselves to the results upon cattle, those for horses 
and for swine being more or less fragmentary and uncertain. By 
far the larger proportion of the results above tabulated, as well 
as the most important of them, are based on experiments in 
which additions were made to a basal ration, the computation being 
by difference. As was pointed out in discussing the apparent 
metabolizable energy of the organic matter on previous pages, 
and as was specifically illustrated in the case of one experiment on 



334 PRINCIPLES OF ANIMAL NUTRITION. 

molasses (p. 291), the difference in the metabolizable energy of the 
excreta is the algebraic sum of the differences in the energy of 
methane, urine, and the several proximate ingredients of the feces, 
and some of these differences may be positive and others negative. 
The computations of the metabolizable energy of the organic matter 
as made in the earlier paragraphs give the net result to the animal 
under the condition of the experiment and include all the secondary 
effects upon digestion, etc. 

In the computations here considered Kellner's methods have 
been followed. In the first place the influence of the added feed 
upon the digestibility of the basal ration has been eliminated by 
basing the computation upon the digested matter. Still further, 
such effects as the decrease of the methane excretion in certain of 
the experiments with molasses, oil, and starch, and the diminished 
export of energy in the urine under the influence of starch and ex- 
tracted straw, have not entered into the computation. In other 
words, the endeavor has been to determine the actual amount of 
energy liberated by the breaking down of the molecules of the di- 
gested starch or protein or fat in the organism without regard to 
these various incidental effects; that is, to determine the real and 
not the apparent metabolizable energy. 

Either method of computation would seem to be entirety defensi- 
ble, and our choice between them will be largely determined by 
the point of view. For the purposes of the physiologist, desirous 
of tracing the details of the chemistry and physics of metabolism, 
the results obtained by the latter method will be of more interest. 
On the other hand, the student of nutrition who is especially in- 
terested in the problems of feeding will not fail to note that the 
results thus reached represent, from his standpoint, only a part of 
the truth. They show (barring errors of detail) how much energy 
is liberated in the body from the several nutrients, but the loss or 
saving of energy in the incidental processes constitutes just as real 
a part of the balance of energy which he wishes to determine as the 
energy liberated from the nutrients themselves, and must be taken 
account of in his calculations. Whether this can best be done by 
using some such factors as those just tabulated and then making 
a correction for these incidental gains and losses, or whether the 
method followed in the earlier paragraphs is to be preferred, it 



THE FOOD AS A SOURCE OF ENERGY. 335 

would probably be premature to attempt to decide at present. 
Pending further investigation and experience, however, it should 
be remembered that the figures on p. 332 will give, in most cases, 
too high results for the metabolizable energy of mixed rations, while 
the same thing is still more emphatically true of Rubner's factors. 

One additional point requires mention. In discussing the 
metabolizable energy of protein it was pointed out (p. 320) that 
it is at least a plausible hypothesis that the proteids are metabo- 
lized in the herbivora substantially as in carnivora, and that the 
excess of energy in the urine is derived from the non-nitrogenous 
ingredients of the food. If we accept this hypothesis, however, 
and assume the metabolizable energy of protein (N X 6.25) to 
be in the neighborhood of 4.9 Cals. per gram, then the figures 
for the non-nitrogenous nutrients are subject to a still further 
deduction, especially in the case of coarse fodders. If we were to 
assign to the fat its full value as given, it would not be difficult to 
compute the metabolizable energy of the carbohydrates on this 
basis, and probably a set of factors could be worked out which 
would correspond to the actual results obtained with mixed rations. 
These, however, if successfully obtained, would be substantially 
identical with the results given on previous pages for the apparent 
metabolizable energy of total or of digestible organic matter, and 
it does not appear that the former would offer, sufficient advantages 
over the latter to justify the labor involved in their computation. 



CHAPTER XI. 

INTERNAL WORK. 

§ i. The Expenditure of Energy by the Body. 

Having considered the food in the light of a supply of energy 
to the animal, it now becomes desirable to take a more general 
view of the subject and inquire into the uses to which the energy 
of the food is applied in the organism. 

We have already distinguished between that portion of the 
potential energy of the food which is convertible into kinetic energy 
in the body, and which we have here called metabolizable energy, 
and that portion of it which is rejected for one reason or another 
in the potential form in the various excreta. This latter portion 
we may dismiss from consideration for the present. The former 
portion — the metabolizable energy — as common experience informs 
us, is applied to two main purposes. First, it supplies the energy 
for carrying on the various activities of the body. Second, if the 
supply is in excess of the requirements of the body a portion of it 
may temporarily escape conversion into the kinetic form and be 
stored up as gain of tissue, notably of fat. We may say briefly, 
then, that the metabolizable energy of the food is used, first, for 
the production of " physiological work " and second, for the storage 
of energy. 

Physiological Work. — The term " physiological work " in the 
previous sentence is employed in a somewhat loose and general 
sense to designate all those activities in the body which are sus- 
tained by the metabolizable energy of the food and whose ultimate 
result is the production of heat or motion. A more definite idea 
of what the term includes may be gained by a consideration of the 
chief factors which go to make up the physiological work of the 
body. 

336 



INTERNAL WORK. 337 

Work of the Voluntary Muscles. — The most obvious form 
of physiological work is that performed by the contraction of the 
voluntary muscles, either in the performance of useful work or in 
the various incidental movements made during the waking hours. 
In a sense the production of muscular work may be said to be the 
chief end of the metabolizable energy of the food, inasmuch as 
all the other activities of the body (apart from the reproductive 
functions and, of course, from mental activities) are accessory to 
this. In amount, however, the energy of muscular work is much 
less than the energy expended in other forms of physiological work 
and consumes a comparatively small percentage of the metaboliz- 
able energy of the food. 

Internal Work. — The body of an animal in what we commonly 
speak of as a state of rest is still performing a large amount of work. 
The most evident forms of this are the work of circulation and res- 
piration. In addition to these, however, there are less obvious kinds 
of work whose total is probably very considerable. The body is an 
aggregate of living cells. The living cell, however, is constantly 
carrying on activities of various sorts, and these activities require 
a supply of energy, although how much of the energy of the food 
is consumed in the various processes of secretion, osmosis, karyoki- 
nesis, etc., it is difficult to say. 

In the numerous varieties of internal work the energy involved 
passes through various forms. Ultimately, however, since it 
accomplishes no work upon the surroundings of the animal, it 
is converted into heat and leaves the body either by radiation and 
conduction, as the latent heat of water vapor or as the sensible 
heat of the excreta. 

Work of Digestion and Assimilation. — Logically the work 
of digestion and assimilation would be classed as part of the internal 
work of the body, but motives of convenience make it desirable to 
consider it separately. 

In a fasting animal, with the digestive tract empty, the various 
forms of internal work indicated above go on with a considerable 
degree of constancy, and the resulting heat production is quite 
uniform under like conditions. If food be given to such an animal 
there results very promptly an increase in the excretion of carbon 



338 PRINCIPLES OF ANIMAL NUTRITION. 

dioxide and the absorption of oxygen and in the amount of heat 
produced. In general terms this is brought about in four ways: 

First, the muscular work required for masticating and swallow- 
ing the food and moving it through the digestive apparatus involves 
an expenditure of energy which finally gives rise to the evolution 
of heat. 

Second, the activity of the various secreting glands of the diges- 
tive tract is stimulated, again making a demand for energy and 
giving rise to an increased heat production. 

Third, the work of the resorbing cells likewise makes demand 
for energy. 

Fourth, the various fermentations, cleavages, hydrations, and 
syntheses which the food ingredients undergo in the course of diges- 
tion, resorption, and assimilation may occasion in individual cases 
either an evolution or an absorption of energy, but taken as a whole 
result in the production of a greater or less amount of heat and con- 
sume a corresponding amount of the metabolizable energy of the food. 

Production of Heat. — The body temperature of the healthy 
warm-blooded animal is practically constant, any considerable 
variation from the average indicating some serious disturbance of 
the animal economy. Since this temperature is ordinarily higher 
than that of the environment, a continual production of heat is 
necessary to maintain it. 

As stated above, the various forms of internal work, including 
the work of digestion and assimilation, give rise in the aggregate 
to the evolution of a large amount of heat, and this heat is of course 
available for the maintenance of the body temperature. 

Whether its amount is sufficient for this purpose, or whether 
under any or all circumstances there is a production of heat for its 
own sake, simply to keep the animal warm, is still a debatable 
question. Many eminent physiologists, notably Chauveau and 
his associates, hold that the primary function of metabolism is to 
furnish energy for the physiological processes going on in the body. 
They hold that the potential energy of the food is converted imme- 
diately into some form of physiological energy, which in its turn, 
in fulfilling its functions, is converted into heat which serves inci- 
dentally to maintain the body temperature. In other words, they 
regard heat as substantially an excretion and would consider that 



INTERNAL WORK. 



339 



in the course of organic evolution those forms have survived in 
which the incidental heat production was sufficient to meet the 
demand of the environment. 

Other physiologists no less eminent hold that at least an ex- 
ceptional demand for heat (low external temperature) may be met 
by a direct combustion of food or body material for that purpose. 
We shall have occasion later to give further consideration to these 
divergent views. 

Summary. — The following scheme may serve to summarize 
what has been said above regarding the uses to which the energy of 
the food is put in the body, the possible direct heat production being 
considered, for convenience, as part of the physiological work of 
the body in order to include it among the other forms of the 
expenditure of energy : 

Energy of excreta. 



Gross energy 



Metabolizable 
energy 



" Physiological 
work 



Work of voluntary 
muscles. 

Internal work. 

Work of digestion and 
assimilation. 



Heat production. 
s Storage of energy. 

For the sake of directness of statement, language has been used 
above which seems to imply that the food is directly oxidized some- 
what like the fuel in a locomotive. While statistically the effect is 
the same as if this were the case, it must not be forgotten that the 
body itself constitutes a reservoir of potential energy and that 
the energy liberated in its various activities comes primarily from 
the potential energy stored up in its various tissues, while the func- 
tion of the food is to make good the loss this occasioned. 

The metabolism of matter and energy in the body might be 
compared to the exchange of water in a mill-pond. The water in 
the pond may represent the materials of the body itself, while the 
water running in at the upper end represents the supply of matter 
and energy in the food, and that going down the flume to the mill- 
wheel the metabolism required for the production of physiological 
work as above defined. The water flowing into the pond does not 
immediately turn the wheel, but becomes part of the pond and 
loses its identity. Part of it may be drawn into the main current 



340 PRINCIPLES OF ANIMAL NUTRITION. 

and enter the flume comparatively soon, while another part may 
remain in the pond for a long time. Pursuing the comparison still 
further, as but a small proportion of the energy liberated in the de- 
scent of the water in the flume takes the form of mechanical energy, 
most of it being converted into heat, so in the body but a small 
proportion of the energy expended in physiological work takes 
ultimately the form of mechanical energy. Finally, if we compare 
the flow of water in the stream below the dam to the heat produc- 
tion of the body, that flow may be increased, in case of need, in two 
ways, viz., by opening the gate wider and letting more water pass 
through the flume (increase of physiological work) or by lowering 
the dam and allowing more water to flow over, corresponding to a 
heat production for its own sake, if such takes place. 

The succeeding sections of this chapter will be devoted to a con- 
sideration of the expenditure of energy in the various forms of in- 
ternal work, including that of digestion and assimilation, while the 
subjects of the production of external work and of J the storage of 
energy may be more appropriately considered in subsequent chap- 
ters. 

§ 2. The Fasting Metabolism. 

If an animal be deprived of food for a sufficient length of time 
to empty the digestive tract, and kept in a state of rest as regards 
muscular exertion, the expenditure of energy in external work and 
in the work of digestion and assimilation are both eliminated, while 
there can be, of course, no storage of energy. Under these condi- 
tions the metabolism of energy in the organism is confined to the 
maintenance of those essential vital activities which were grouped 
above under the term " internal work " in the narrower sense, to- 
gether with any direct production of heat for its own sake. The 
fasting animal, then, affords the most favorable opportunity to 
study the laws governing the expenditure of energy for the internal 
work of the body. The fasting metabolism has already been con- 
sidered in Part I from the side of the matter involved; here we are 
concerned with its energy relations. 

Nature of Demands for Energy. 

Without attempting to enter into details, it may be said that 
the internal work of the fasting organism may be roughly classified 



INTERNAL WORK. 341 

as muscular, glandular, and cellular. To the demand for energy 
for these purposes we have probably to add, at least in some cases, 
a direct demand for heat production. 

Muscular Work. — The more obvious forms of muscular work 
in the quiescent animal are circulation and respiration. To these 
are to be added as minor factors any movements of other in- 
ternal organs, and especially the general tonus of the muscular 
system, while finally, the various incidental movements made by 
such an animal, although not logically belonging in the category 
of internal work, practically have to be classed there in actual 
experimentation. It would be aside from the purpose of this 
volume to enter into any detailed consideration of these forms of 
internal work, but a few general statements regarding their amount 
may be of interest. 

Circulation. — The work performed by the heart is determined 
by two factors, viz., the weight of the blood moved and the mean 
arterial pressure overcome. Quite divergent results have been ob- 
tained by various investigators for the former factor, while the 
latter is more readily determinable. Zuntz & Hagemann * estimate 
the output of blood by the heart of the horse from a comparison 
between the blood gases and the respiratory exchange, and compute 
the expenditure of energy in circulation to be 5.01 per cent, of the 
total metabolism of the horse in a state of rest and 3.77 per cent, 
during moderate work. Hill f estimates the average work of the 
heart in man at about 24,000 kilogram-meters in twenty-four hours. 
As the velocity of the circulation increases, the friction in the pe- 
ripheral blood-vessels, and consequently the arterial pressure, rap- 
idly augments, so that in case of severe muscular exertion, for ex- 
ample, the work of the heart may readily become excessive. 

Respiration. — The work of respiration consists essentially of 
an expansion of the thorax against the resistance caused by the 
atmospheric pressure and the elasticity of the lungs and the rib 
cartilages. Zuntz & Hagemann J estimate its amount in the 
horse at about 4.7 per cent, of the total metabolism. 

Muscular Tonus. — As was pointed out in Chapter VI, the living 

* Landw. Jahrb., 27, Supp. Ill, 371. 

t Schaffer's Text-book of Physiology, II, 43. 

% Loc. cit. 



H 2 



PRINCIPLES OF ANIMAL NUTRITION. 



muscle is in a constant state of slight tension or tonus, and is con- 
stantly the seat of metabolic activities which we may presume 
serve, in part at least, to maintain that tonus. This is, of course, 
equivalent to saying that there is a continual liberation of kinetic 
energy in the resting muscle, which temporarily takes the form of 
muscular elasticity but ultimately appears as heat. As to the 
amount of energy thus liberated exact information seems to be lack- 
ing, but in view of the relatively large mass of the muscles as com- 
pared with that of the other active tissues we may assume that it 
is not inconsiderable. The same thing would seem to be indicated 
also, as noted in Chapter VI (p. 191), by the great decrease in the 
metabolism and heat production ordinarily observed as the result 
of paralysis of the motor nerves by curari. 

Incidental Muscular Work. — It is rare that an animal, even 
when at rest in the ordinary sense, does not execute more or less 
motions of various parts of the body, all of which involve a conver- 
sion of potential energy into the kinetic form. Even apparently 
insignificant movements may materially increase the amount of 
metabolism. Zuntz & Hagemann,* for example, report a respira- 
tion experiment upon a horse in which the uneasiness caused by the 
presence of a few flies in the chamber of the apparatus caused an 
increase of over 10 per cent, in the metabolism. Johanson, Lan- 
dergren, Sonden & Tigerstedt,f in two-hour periods, found the fol- 
lowing average and minimum values per day and kilogram weight 
for the excretion of carbon dioxide by a fasting man during sleep, 
the results plainly showing the increased metabolism due to rest- 
lessness : 





Average, 
Grms. 


Minimum, 
Grms. 


Third day (first day of fasting) 


7.296 
7.704 
8.136 
7.488 
7.212 


6.744 


Fourth " 


6.768 


Fifth " (very restless) 


7.524 




6.684 


Seventh " 


6.564 







Subsequently Johanson % compared the excretion of carbon 
dioxide by a fasting man when simply lying in bed (awake) with 

* Landw. Jahrb., 23, 161. 

t Skand. Arch. f. Physiol., 7, 29. 

% Ibid., 8, 85. 



INTERNAL WORK. 



343 



that obtained when all the muscles were as perfectly relaxed as 
possible. The results per hour were : 

Lying in bed 24 . 94 grams 

Complete muscular relaxation 20.72 " 

Furthermore, there is more or less muscular exertion involved 
during the waking hours in maintaining the relative position of the 
different members of the body. This is notably true of the effort 
of standing. In experiments with the respiration-calorimeter 
under the writer's direction* the heat production of a steer per 
minute while standing and lying was found to be approximately 
as follows: 





Lying. 
Cals. 


Standing. 
Cals. 


Ratio, Lying to 
Standing. 


Period A 


5.322 
5.781 
6.310 
6.605 


7.031 
7.700 

8.177 
8.495 


1 : 1 321 


" B 

" C 


1 : 1.332 
1 : 1 296 


" D 


1 : 1.286 



Zuntz t found an even greater difference in the case of the dog, 
the average oxygen consumption per minute being — 

Lying 174.3 c.c. 

Standing 245.6 " 

In experiments of any considerable duration on normal animals 
it is impossible to avoid more or less expenditure of energy in this 
incidental muscular work, while it is often a matter of difficulty 
to make the different periods of an experiment comparable in this 
respect. 

Glandular Work. — The activity of the various secretory, ab- 
sorptive, and excretory organs may be conveniently summarized 
under this head. While the purpose of the glandular metabolism 
is, in the majority of cases, primarily a chemical one, the accom- 
plishment of this purpose involves an expenditure of energy which, 

* Proc. Soc Prom. Agr. Sci , 1902. 
f Arch. ges. Physiol , 68, 191. 



344 PRINCIPLES OF ANIMAL NUTRITION. 

so far as it is not removed from the body in the potential form in 
the secretions or excretions, ultimately takes the form of heat. 

Moreover, the fundamental features of glandular metabolism 
appear to be indentical with those of muscular metabolism. Thus 
Henderson * has shown that the active submaxillary gland of the 
dog does not lose nitrogen as compared with the inactive gland, 
but does lose weight, evidently from the metabolism of non- 
nitrogenous matter. Similarly, Bancroft t found the respiratory 
exchange of the same gland during activity to be three or four times 
that during rest. If we may accept these results as typical, we 
must conclude that glandular, like muscular metabolism is largely 
at the expense of non-nitrogenous matter, and shall not hesitate to 
summarize the two together as parts of the internal work of the 
body. 

Cellular Work. — While both muscular and glandular work 
are forms of cell activity, a passing mention may be made for the 
sake of completeness of such processes as imbibition, filtration, 
osmosis, protoplasmic motion, karyokinesis, etc., which, while 
taking place in the various organs, are so general in their nature and 
form so essential a part of our conception of cell life that it seems 
proper to speak of them collectively as cellular work. As to the 
quantitative importance of these activities, so far as they can be 
differentiated from the special functions of the various organs, we 
lack the data for forming any definite conception, although it 
would appear that it must be small. 

Heat Production. 

As we have just seen, the forms of internal work are numerous 
and some of them are not readily accessible to measurement. All 
of them, however, have this in common, that the energy used in 
their performance ultimately assumes the form of heat. 

This being the case, while the single factors making up the 
internal work are not readily determined, a determination of the 
total heat produced by a fasting animal in a state of rest (either 
directly or by computation from the amount and kind of matter 
metabolized) will show the total amount of energy consumed in the 

* Am. Jour. Physiol., 3, 19. f Journal of Physiol , 27, 31. 



INTERNAL WORK. 



345 



performance of the internal work and how it varies under varying 
conditions. Carnivorous animals, with their short and relatively 
simply digestive canal, lend themselves most readily to experiments 
of this sort although rabbits and guinea-pigs have been employed 
to some extent, as well as, for short periods, men. 

Constancy Under Uniform Conditions. — Attention has al- 
ready been called in Chapter IV to the relative constancy of the 
total metabolism of the fasting animal, particularly as compared 
with the total mass of active tissue in the body. This constancy 
has been especially emphasized by Rubner,* and forms the basis 
of his determinations of the replacement values of the several 
nutrients which will be considered in the following chapter. 
With a rabbit the following daily averages, computed per 100 
parts of nitrogen in the body, were obtained: 



Day of Experiment. 


Nitrogen in 
Urine. 


Fat 
Metabolized. 


Third to eighth 


2.16 
2.19 


16.2 
13.8 


Ninth to fifteenth 





Since the ratio of proteids to fat metabolized did not vary 
greatfy in these trials, the total amount of carbon dioxide ex- 
creted may be taken as an approximately accurate measure of 
the total metabolism. For the several days of the experiment, 
this was as follows: 





Average Live 

Weight, 

Grms. 


Carbon Dioxide Excreted. 


Day. 


Per Head, 
Grms. 


Per Kg. 

Live Weight, 
Grms. 


Fifth 


2091 
2002 
1907 
1864 
1764 
1731 
1716 
1697 


36.1 
31.8 
30.3 
29.2 
30.2 
27.4 
27.4 
25.5 


17 26 


Seventh 


15 90 


Ninth 


15.90 


Tenth 

Twelfth 


15.65 
17.18 


Thirteenth 

Fourteenth 

Fifteenth 


15.81 
15.95 
15.90 







* Zeit. f. Biol., 17, 214; 19, 312. 



34^ PRINCIPLES OF ANIMAL NUTRITION. 

With a dog the following results were obtained : 



Day. 



Live 


Nitrogen 


Weight, 


in Urine, 


Grms. 


Grms. 


9190 


4.23 


8920 


2.89 


8620 


3.65 


8190 


2.59 


8030 


2.41 


7890 


2.53 


7970 


2.98 


7830 


3.02 



Fat 
Metab- 
olized, 
Grms. 



Carbon Dioxide 
Excreted. 



Per Head, 
Grms. 



Per Kg. 

Live 
Weight, 
Grms. 



First 

Second 

Fourth 

Tenth 

Eleventh .. 
Twelfth . . . 
Thirteenth 
Fourteenth 



51.74 
45.94 
42.90 
45.55 
41.83 
36.48 
37.45 
33.80 



187.4 
157.5 
146.9 
151.7 
140.4 
127.9 
134.8 
125.0 



20.70 
17.83 
17.99 
18.70 
17.86 
16.13 
17.06 
16.12 



Rubner also quotes the following results by Kuckein on a cock:: 

~ Carbon Dioxide per 

D& y- Kg. Live Weight. 

Third 21 .73 grams. 

Fifth 21.47 " 

Seventh 21.43 " 

Rubner 's experiments on a guinea-pig * show a similar constancy, 
the heat production being computed from the total metabolism: 

Heat Production 
y- per Kilogram. 

First 149.9 Cals. 

Second 162.6 " 

Third 156.5 " 

Fourth 140.5 " 

Fifth 137.3 " 

Sixth 150.6 " 

Seventh 157.4 " 

Eighth 155.6 " 

Ninth 162.6 " 

Concerning this point Rubner says : f " The uniformity of the 
fasting metabolism proves that, in spite of the undoubted limita- 
tation of all the voluntary functions which can cause a consump- 
tion of matter, no further reduction of the metabolism is possible, 
* Biologische Gesetze, p. 15. t Loc. cit., 19, 326. 



INTERNAL WORK. 347 

and we recognize from this that we have to do here with a constant 
metabolism which is indissolubly connected with life itself. The 
animal in the fasting state adjusts itself to the minimum metabolism. " 

In other words, the metabolism and consequent heat production 
of the fasting, quiescent animal speedily reaches a minimum which 
represents the aggregate demands of the vital activities of the 
organism for energy ; that is, which represents the internal work of 
the body in the sense in which the words are here used, plus the 
metabolism required for any direct production of heat which may 
be necessary to maintain the normal temperature of the animal. 

The relative importance of the internal work in the narrower 
sense and of the direct heat production as regards their demands for 
a supply of energy will appear more clearly when we consider, in 
the following paragraphs, the effects of varying conditions, and 
particularly of the thermal environment, upon the heat produc- 
tion of the fasting animal. 

Influence of Thermal Environment on Heat Production.* — An 
animal, particularly in the temperate zones, is subject to consider- 
able variations of external conditions, particularly of temperature, 
which, in the first place, tend to affect the rate at which it emits 
heat, and secondarily, within certain limits to modify the amount 
of heat produced in the body. 

Body Temperature. — As regards their body temperature, 
animals have been divided into two great classes : the cold-blooded 
(poikilothermic), whose temperature as a rule differs but slightly 
from that of their surroundings, and the warm-blooded (homoio- 
thermic), whose temperature remains approximately constant dur- 
ing health whatever be that of their surroundings. Since all our 
domestic animals, as well as man himself, belong to the second 
group, it alone will be considered in the following paragraphs. 

Since the animal is constantly producing heat in the various 
ways already indicated, it is obvious that in order to maintain a 
constant body temperature it must be able to give off this heat at 
the same average rate at which it is produced. Iianke illustrates 
this necessity in a striking manner by computing that if the 

* The discussion of this subject follows to a considerable extent that of 
Iianke in the introduction to his "Einwirkung des Tropenklimas auf die 
Ernahrung des Menschen," Berlin, 1900. 



348 PRINCIPLES OF ANIMAL NUTRITION. 

body of a man were unable to give off the heat which it pro- 
duces, a single day would suffice to raise it to a pasteurizing 
temperature, while in the course of a year, at the same rate, a 
temperature of over 17,000° C. would be reached. 

Furthermore, since the external conditions of temperature are 
subject to frequent and sudden changes, it is obvious that the 
balance between heat production and emission must be capable of 
prompt adjustment to varying circumstances. 

Thermic Range. — The ability of the animal body to adapt 
itself to changes qf temperature has, however, often been ex- 
aggerated. As a matter of fact this adaptation is possible only 
within a comparatively narrow range, and unless we hold fast to 
this fundamental idea we are in danger of reaching fallacious 
and absurd conclusions. Man has considerably extended the range 
of climate within which he can exist by means of clothing, shelter, 
artificial heat, and even to a slight extent artificial refrigeration, 
and this fact often leads unconsciously to an overestimate of the 
possible thermic range. These means of artificial protection re- 
sult essentially in modifying the temperature to which the body is 
actually exposed, and the same is true in a less degree of the differ- 
ences in the summer and winter coats of animals. The fact still 
remains that the actual thermic range of any species is and must be 
strictly limited. All life implies a certain amount of metabolism, 
and consequently of heat production. With rising temperature a 
point must sooner or later be reached at which the animal is unable 
to impart tnis heat to its surroundings as fast as it is produced, and 
in which the rise in temperature necessarily resulting will prove 
fatal. With falling temperature a point will be reached at which 
the greatest possible amount of metabolism in the body will be 
unable to equal the rate at which heat is lost to the surroundings 
and the animal will perish from cold. Both the maximum and 
minimum points and the extent of the thermic range will vary for 
different species and varieties of animals, but at best the range is 
relatively small. 

Means of Regulation. — Within the thermic range of a given 
animal the adjustment to its thermal environment may be effected 
in one or both of two ways, viz., by a regulation of the rate of emis- 
sion of heat or by a variation in the heat production. 



INTERNAL WORK. 349 

Regulation of Rate of Emission. — Heat is given off by the body 
in four principal ways: (1) by conduction; (2) by radiation; (3) 
by evaporation of water; (4) as the sensible heat of the excreta. 

By conduction, heat is transferred directly from the body to 
its surroundings, including such solid objects as it may be in con- 
tact with and particularly the air. The rate of loss in this way 
will depend upon the relative temperature and conductivity of 
the surface of the body and of the substances with which it is in 
contact, and in case of the air will be also influenced by the rate 
of motion of the latter relatively to that of the body. 

By radiation, a constant exchange of heat goes on between the 
body and objects not in immediate contact with it. Since the body 
is usually warmer than its surroundings, the net result of this ex- 
change is a loss of heat by the body, the amount of which depends 
upon the specific radiating power of the surface of the body and 
upon the difference in temperature between the latter and sur- 
rounding objects. 

By evaporation of water from the skin, and to a less degree 
from the mucous membrane of the air-passages, a large amount 
of heat may be removed as latent heat of vaporization. The 
amount of water evaporated from the skin, and consequently the 
rate at which heat is carried off, will depend in part on the 
amount transpired by the skin, but when this is abundant, 
chiefly upon the relative humidity of the air and upon its rate of 
movement. 

Finally, the heat removed in the excreta is relatively small, and 
in the case of the fasting animal in particular is insignificant as 
compared with the losses through the other three channels. 

In general we may say that the rate of emission of heat in all 
of the first three ways named is determined by two sets of condi- 
tions, viz., those relating to the environment of the animal (tem- 
perature, relative humidity, movement of air) and those relating 
to the animal itself and particularly to its surface. 

The conditions of the first set, of course, are beyond the control 
of the organism. Their tendency is to produce the same effect upon 
the rate of emission of heat that they would upon that of a lifeless 
body, viz., to increase it as the temperature of the surroundings is 
lowered and their conducting power increased. In the case of the 



35° PRINCIPLES OF ANIMAL NUTRITION. 

living animal this tendency is offset by the regulative mechanism 
acting upon the second set of conditions, so that, e.g., a fall in 
the temperature of its surroundings within certain limits instead 
of increasing the rate of emission, as in the case of a lifeless body, 
has no effect upon it. This regulation of the rate of emission is 
effected chiefly by means of changes in the temperature and state 
of moisture of the skin, brought about on the one hand through the 
vaso-motor mechanism and on the other through the special nerves 
of perspiration. 

Variations of external temperature acting upon the peripheral 
nerves influence by reflex action the activity of the vaso-motor 
nerves which regulate the caliber of the minute blood-vessels. 
Exposure to cold causes a contraction of the capillaries of the 
skin and a relaxation of those of the viscera. As a result more 
blood passes through the latter, while the flow through the skin 
is diminished, the latter becomes paler, and since the heat given 
off is not fully replaced by the blood current, its temperature falls. 
Exposure to heat has the contrary effect. The capillaries of the 
skin relax, more blood flows through them, the skin becomes flushed 
and its temperature rises, while the flow of blood to the viscera is 
checked. A fall in the temperature of the skin, however, tends to 
diminish the rate of emission of heat both by conduction and radia- 
tion, while a rise in its temperature has the opposite effect, thus 
counteracting the tendency of changes of external temperature. 
Tn other words, the "emission constant" of the skin changes to 
meet changes in external conditions. So exactly are these mech- 
anisms adjusted in health that within certain rather narrow limits 
they maintain the rate of emission of heat, and consequently the 
average temperature of the body, very nearly constant. 

Obviously, however, there must be a limit above which the 
temperature and radiating power of the skin cannot be increased 
to compensate for a rise in external temperature. The second 
method of regulation then comes more markedly into play through 
the familiar act of perspiration, or sweating. At high temperatures 
the activity of the sweat-glands is greatly stimulated, in part 
doubtless by the more abundant supply of blood to the skin, but 
chiefly by reflex stimulation of the special nerves which control the 
secretion of sweat. The evaporation of the relatively large amount 



INTERNAL WORK. 



351 



of water thus supplied to the surface of the skin is a powerful means 
of refrigeration, as we know no less from common experience than 
from scientific determinations, the evaporation of a single gram of 
water requiring approximately 0.592 Cal. of heat. With very- 
high temperatures, especially in a humid atmosphere, however, 
even this method of disposing of the heat becomes insufficient and 
the extreme upper limit of the thermal range is passed. 

These two methods of regulation of the body temperature are 
often spoken of collectively as "physical" regulation. 

Variations in Amount of Heat Produced. — Just as there is a 
superior limit beyond which the regulation of the body tempera- 
ture by the means above described cannot be carried, so it is obvious 
that there must be a lower limit ,of regulation. However much the 
cutaneous circulation may be reduced, the skin will always lose heat 
to a sufficiently cold environment faster than it is being generated 
by the internal work of the body. Under these circumstances the 
only method by which the temperature of the animal can be main- 
tained is an increase in the rate of generation of heat. 

That changes of external temperature affect the amount of heat 
generated was shown by the experiments of Lavoisier and the 
observations of Liebig, but Liebermeister * appears to have been 
the first to clearly enunciate the theory of regulation by variations 
in the rate of production. The fact of such regulation has been 
fully demonstrated by numerous subsequent investigators. As a 
typical example we may take the well-known experiments of Theo- 
dor f on a cat, some of the results of which are as follows : 



Temperature, 
Deg. 
Cent. 


CarbonDioxide 
Excreted, 

Grms. 


Oxygen 

Taken Up, 

Grms. 


Temperature, 
Deg. 

Cent. 


CarbonDioxide 

Excreted, 

Grms. 


Oxygen 

Taken Up, 

Grms. 


-5.5 

-3.0 

0.2 

5.0 


19.83 
18.42 
18.24 
17.90 


17.48 
18.26 
19.95 
14.82 


12.3 
16.3 
20.1 
29.6 


17.63 
15.73 
14.34 
13.12 


17.71 
14.74 

12.78 
10.87 



Numerous other investigators have obtained similar results, 
but the effect of low temperature in stimulating the heat produc- 
tion of warm-blooded animals is too well established to require an 

* Arch f. (Anat. u.) Physiol., 1860, pp. 520 and 589; 1861, p. 661. 
t Zeit. f. Biol., 14, 51. 



35 2 



PRINCIPLES OF ANIMAL NUTRITION. 



extended citation of authorities here. Some of Rubner's * more 
recent results, however, are of interest as showing the delicacy of 
the reaction. The experiments were made on fasting dogs in a 
state of complete rest, the heat production being computed from 
the total metabolism of carbon and nitrogen : 

Tempera- Heat Production per 

ture, Deg. C. Kg. in 24 Hours. 

13.8 78.68 Cals. 

j 14.9 74.74 

L l 17.3 69.78 

^18.0 67.06 



II 



11.8 40.60 

12.9 39.13 

15.9 35.99 

117.5 35.22 



(13.4 39.65 

III] 19.5 35.10 

(27.4 30.82 

This method of regulation of the body temperature is often briefly 
designated as " chemical " regulation. 

Just how the additional generation of heat is effected is not so 
clear. From the fact that the muscles are the seat of a very large 
part of the heat production of the body we should naturally be 
inclined to look to them as the source of the increase. In quite a 
number of experiments on man, of which those of A. Loewy f and 
of Johansson % may be especially mentioned, a stimulation of the 
heat production with falling temperature was only observed when 
there was visible muscular action, such as shivering, while in the 
other cases only the " physical " regulation occurred. Any contrac- 
tion of the muscles would of course be a source of heat, but the in- 
crease with falling external temperature has been repeatedly observed 
with animals in the absence of this obvious cause. Whether in 
such cases there is an increase in the tonus of the muscles, involv- 
ing an increase in their metabolism, or whether, through some 
form of reflex stimulation, the rate of oxidation is accelerated 
* Biologische Gesetze, p. 10. 
t Arch. ges. Physiol., 46, 189. 
% Skand. Arch. f. Physiol., 7, 123. 



INTERNAL WORK. 



353 



simply for the sake of the heat produced is still an unsettled ques- 
tion and one which, for our present purpose, we need not pause 
to consider. As to the fact of the increase there is no question. 

Critical Temperature. — In early writings upon this subject 
the influence of external temperature in increasing or diminishing 
the heat production of the body was frequently spoken of as if it 
were of unlimited application, and the same idea has passed more 
or less fully into the popular literature of the subject. But little 
reflection is necessary, however, to show that this cannot be the 
case. Common observation teaches us that neither our own metab- 
olism nor that of our domestic animals, as roughly measured by 
the consumption of food, is affected, for example, by the difference 
between winter and summer to any such extent as would correspond 
to the difference in average temperature. Moreover, if every rise 
in external temperature diminished the heat production, there 
would be a temperature at which no heat production at all would 
occur and at which, therefore, life could exist without metabolism, 
which is a contradiction in terms. This extreme case renders clear 
the fundamental error of this view, viz., that of regarding the heat 
production as an end in itself and not as, substantially, an incident 
of the general metabolism. 

Carl Voit* was the first to demonstrate by exact scientific 
experiments the limits within which the influence of temperature 
upon metabolism (the so-called chemical regulation) is confined. 
His experiments were a continuation of those of Theodor (p. 351), 
and were made upon a man weighing about 70 kgs. and wearing 
ordinary clothing. After exposure for some time to the tempera- 
ture to be tested he passed six hours in the chamber of the respira- 
tion apparatus, fasting and in complete rest. During the six hours 
the excretion of carbon dioxide and nitrogen was as follows: 



Temperature. 
Deg. C. 


Carbon 
Dioxide. 

Grms. 


Urinary 

Nitrogen 

Grms. 


Temperature. 
Deg. C. 


Carbon 

Dioxide. 

Grms. 


Urinary 

Nitrogen. 

Grms. 


4.4 

6.5 

9.0 

14.3 

16.2 


210.7 
206.0 
192.0 
155.1 
158.3 


4.23 
4.05 
4.20 
3.81 
4.00 


23.7 
24.2 

26.7 
30.0 


164.8 
166.5 
160.0 
170.6 


3.40 
3.34 
3.97 



* Zeit. f. Biol., 14, 57. 



354 



PRINCIPLES OF ANIMAL NUTRITION. 



Later and more comprehensive experiments with animals by 
Rubner have given corresponding results. Thus with two guinea- 
pigs the following figures were obtained in 24-hour experi- 
ments : * 



Mature Animal. 


Young Animal. 


Temperature 
of Air, 
Deg. C. 


Temperature 

of Animal, 

Deg. C. 


C0 3 per Kg. 

and Hour, 

Grms. 


Temperature 
of Air, 
Deg. C. 


Temperature 

of Animal, 

Deg. C. 


CO a per Kg. 

and Hour, 

Grms. 





37.0 


2.905 





38.7 


4.500 


11.1 


37.2 


2.151 


10 


38.6 


3.433 


20.8 


37.4 


1.766 


20 


38.6 


2.283 


25.7 


37.0 


1.540 


30 


38.7 


1.778 


30.3 


37.7 


1.317 


35 


39.2 


2.266 


34.9 


38.2 


1.273 








40.0 


39.5 


1.454 









A later experiment by Rubner f upon a dog, in which the heat 
production was measured by a calorimeter, gave the following 
results : 

Temperature of Air. Heat Production per Kg. 

7.6° C 83.5 Cals. 

15.0° " 63.0 " 

20.0° " 53.5 " 

25.0° " 54.2 " 

30.0° " 56.2 " 



The uniform testimony of these various experiments is that for 
each species there is a certain external temperature at which the 
metabolism and consequent heat production reach a minimum. 
With man in ordinary clothing it would appear to lie at about 
15° C.,% with the dog at about 20° C, and with the guinea-pig at 
about 30°-35° C. Below this point the heat production rises or 
falls with changes of external temperature; or, in other words, the 
constancy of the body temperature is secured, in part at least, by 

* Biologische Gesetze, p. 13. 

f Archiv f. Hygiene, 11, 285. 

% Rubner (Biol. Gesetze, p. 30) says that for naked man it is about 37° C. 



INTERNAL WORK. 355 

means of the so-called " chemical " regulation, that is, by variations 
in the production of heat. 

Above this point the heat production, instead of a further de- 
crease, shows an increase, which, however, is slight as compared 
with the differences observed as a result of the "chemical" regu- 
lation. Here we are obviously in the domain of the "physical" 
regulation — the regulation by changes in the emission constant of 
the skin. This temperature at which the chemical regulation 
ceases, and which presumably varies for different species of animals, 
Ranke calls the critical temperature. Below it the regulation is 
chiefly "chemical," above it chiefly "physical." The slight in- 
crease in the metabolism above the critical point is plausibly ex- 
plained as due to the greater activity of the organs of circulation, 
respiration, and perspiration required for the "physical" regula- 
tion. 

Rubner's experiments also show that the portion of the thermic 
range lying above the critical temperature falls into two distinct 
subdivisions. For a certain distance above that point, the factors 
chiefly concerned in the regulation of the body temperature are 
conduction and radiation, which keep pace with the rising tem- 
perature in the manner already explained. At the same time, 
there is a small increase in the rate of evaporation of water, approxi- 
mately equivalent to the slight increase in the metabolism above 
the critical temperature to which attention has just been called. 
Matters go on in this way through a certain range of temperature 
until the regulative capacity of the vaso-motor mechanism is 
utilized to its maximum. If the external temperature still rises, 
the emission of heat by conduction and radiation begins to decrease 
as it would in a lifeless object, and the deficit thus occasioned is 
made up by a sudden increase in the exhalation of water vapor, 
coinciding, in man, with the production of visible perspiration. 
This sudden increase in the activity of the sweat-glands is accom- 
panied, as we should expect, by an increase in the total metabolism 
and consequent heat production. 

These phenomena are well illustrated by Rubner's experiments 
with a fasting dog, already partially cited on the opposite page. 
The following table shows the amount of heat carried off by con- 
duction and radiation and as latent heat of water-vapor at the 



356 



PRINCIPLES OF ANIMAL NUTRITION. 



several temperatures, and the same facts are also shown graphically 
in the accompanying diagram. 







Disposed of by- 


Temperature 
of Air, 
Deg. C. 


Total Heat 

Production, 

Cals. 


Conduction 

and 
Radiation, 

Cals. 


As Latent 

Heat of Water 

Vapor, 

Cals. 


7.6 


83.5 


71.7 


11.8 


15.0 


63.0 


49.0 


14.0 


20.0 


53.5 


37.3 


16.2 


25.0 


54.2 


37.3 


16.9 


30.0 


56.2 


30.0 


26.2 




7.6 J C 



15 U C 20 C 25°C 30" C 

It appears, then, that a certain minimum heat production, 
corresponding to the metabolism at the critical temperature, is 
inseparably connected with the life of the animal. The very fact 
that the heat production at this temperature is a minimum shows 
that its amount is not determined by the needs of the organism for 
heat. If the latter were the controlling condition, a rise of exter- 
nal temperature should still further reduce the generation of heat, 
while as a matter of fact it is accompanied by a slight increase up 
to the point where the amount of heat produced overpasses the 
ability of the organism to dispose of it and death results. The 
natural conclusion is that the metabolism at the critical tem- 
perature is that which is necessary for the performance of the 
various functions of the organism, and that the heat production 
at this temperature, therefore, represents the amount of energy 
necessarily consumed in the internal work of the body. This is, 
of course, Rubner's conclusion (p. 346) in a slightly altered form. 

The case is not unlike that of a room in which a fire must be 
kept burning for some purpose — a kitchen, for example. In winter, 
changes in external temperature may be met by burning more or 



INTERNAL WORK. 357 

less fuel. As spring advances, the fire is reduced until it is just 
sufficient for the necessary work. If the weather still continues 
to grow warmer, since the fire cannot be further reduced the excess 
of heat is gotten rid of by opening the windows more or less, while, 
to carry out the analogy, in very hot weather we may sprinkle the 
floor or wet the walls to secure relief from heat through the evapora- 
tion of water. 

Modification of Conception of Critical Temperature. — 
In our discussion thus far we have considered chiefly the influence 
of external temperature on metabolism and heat production. This 
is, however, by no means the only condition affecting the heat 
balance of the body. Of the other meteorological factors, three 
call for special mention, viz., wind, insolation, and in particular 
relative humidity. 

Wind. — In a perfectly still atmosphere, the layer of air next to 
the skin becomes warmed and loaded with water vapor and con- 
stitutes to a certain degree a protective envelope which is removed 
with comparative slowness by gaseous diffusion. A current of air, 
by removing this protecting layer and bringing fresh portions of air 
in contact with the body, increases the emission of heat both by 
conduction and by evaporation of water. This is in accord with the 
common experience that a degree of cold which can readily be 
borne when the air is still becomes intolerable in a brisk wind, while, 
on the other hand, the oppressiveness of a very hot day is sensibly 
relieved by even a slight breeze. The effect of wind, then, is to 
transpose the thermic range of the animal to a higher place in the 
thermometric scale, and to correspondingly raise the critical tem- 
perature. 

Insolation. — The direct rays of the sun impart a considerable 
amount of heat to the body. The effect of insolation, therefore, is 
the reverse of that of wind, viz., to transpose the thermal range 
and the critical temperature downward. A similar effect is pro- 
duced, of course, by the sun's heat when reflected from surrounding 
objects, or by the radiant heat from hot objects, the earth, for ex- 
ample. On the other hand, the radiation from the body into space 
during the night, especially at high altitudes and through a dry, 
clear atmosphere, may have a very considerable effect in the con- 
trary direction. 



35 8 PRINCIPLES OF ANIMAL NUTRITION. 

Relative Humidity. — The relative humidity of the air affects the 
emission of heat in two principal ways. At low temperatures, 
where the evaporation of water plays a subordinate role, it increases 
the rate of emission by increasing the conductivity and specific 
heat of the air, and also the conductivity of the skin and the body 
covering (hair, fleece, clothing), these effects outweighing its in- 
fluence in diminishing the relatively small amount of evaporation 
Moist cold is, therefore, more trying than dry cold. 

At high temperatures, on the other hand, where a large pro- 
portion of the heat is removed by evaporation, a high relative 
humidity i by checking this evaporation, hinders the emission of 
heat, this effect overbalancing any slight increase in conductivity. 
Moist heat is accordingly more oppressive than dry heat. 

An increase in the relative humidity, then, abbreviates the 
thermal range at both ends, while at moderate temperatures it 
appears to have but little effect, a diminution of the loss by evap- 
oration being compensated for by an increase in radiation and 
conduction. 

Critical Thermal Environment. — From the above it is 
obvious that the so-called critical temperature is not a constant, 
even for the same species or the same individual, but that other 
factors than the temperature of -the air materially affect it. 

What is constant (relatively at least) is the rate at which heat 
is produced in the body by the metabolism necessary to sustain its 
various physiological activities, that is, by its internal work In 
order to maintain the normal body temperature, the total outflow 
of heat through its various channels must, at its minimum, be equal 
to the amount thus liberated in the organism. The outflow of 
heat, as we have seen, is affected directly or indirectly by the 
external conditions, and largely by the three just mentioned. In- 
numerable combinations of these conditions are possible, and any 
one of them whose combined effect upon the animal is to make 
the outflow of heat equal to the rate of evolution due to the 
internal work will constitute a critical point in the above sense. 
Any change in such a set of conditions which tends to increase the 
outflow of heat will, like a fall in temperature, be met chiefly by an 
increased heat production. Any change tending in the opposite 
direction will be compensated for by the effects upon the organ- 



INTERNAL WORK. 359 

ism whch have already been described and which result in maintain- 
ing the rate of emission of heat at a point enough higher than before 
to provide for carrying off the extra heat arising from the physio- 
logical work of the regulative mechanism itself. In other words, 
instead of a critical temperature, we get the conception of a critical 
thermal environment, which may be reached under a variety of 
conditions, and below which we have the domain of " chemical " 
regulation, while above it is the region of " physical " regulation. 

Influence of Size of Animal on Heat Production. — The total 
metabolism of a large animal is necessarily greater than that of a 
small one of the same species, but it is not proportional to the 
weight, being relatively greater in the smaller animal under com- 
parable conditions. 

Relation of Heat Production to Surface. — Bergmann * 
appears to have been the first to connect the fact just stated with 
the relatively greater surface of the smaller animal, but we are in- 
debted to Rubner f for the first quantitative investigation of this 
phase of the subject. His experiments were made on six dogs 
whose weights varied from 3 to 24 kilograms each. The total 
metabolism (proteids and fat) of each of these animals in the fasting 
state was determined in from two to thirteen experiments, and 
from their results the average heat production of each animal was 
computed. The table on page 360 \ shows the air temperature and 
the computed heat production per kilogram live weight in each 
experiment, and also the same corrected to the uniform tempera- 
ture of 15° C. This correction is made on the basis of Theodor's 
experiments (see p. 351), according to which a difference of 1° 
Centigrade caused the amount of oxygen taken up by the cat to 
vary 1.11 per cent. The first series consists of a selection from 
Pettenkofer & Voit's experiments. 

Whether we consider the observed or the corrected heat pro- 
duction we find that with the single exception of the corrected 
result for No. VI the amount per unit of live weight increases as the 
weight itself decreases. 

* Cited by Rubner. 

t Zeit. f, Biol , 19, 535. 

% The figures of the table are computed from those given by Rubner in 
loc. cit., p 540, and differ in some cases from the summary given in loc. cit., 
p 542. 



360 



PRINCIPLES OF ANIMAL NUTRITION. 



No. of 


Date. 


Live 

Weight, 

Kgs. 


Air Tem- 
perature, 
Deg. C. 


Heat Production 
per Kg. 


Ani- 
mal. 


Observed, 
Cals. 


Corrected 

to 15°, 

Cals. 


I , 


Pettenkofer & Voit's J 
experiments 

Average 


30.96 
29.87 
31.44 
30.38 


17.1 
17.7 
16.2 
13.9 


38.99 
31.82 
37.39 
36.54 


39.90 
32.77 

37.89 
36.09 




30.66 

24.11 
23.75 
23.27 


16.2 

15.0 
15.0 
15.0 


36.18 

41.40 
40.22 
41.10 


36.66 




June 19, 1883 


41.40 


\ 


" 21, " ... 


40.22 


II J 


" 23, " 


41.10 


1 


Average . . 




I 


23.71 

19.80 
19.01 
18.79 


15.0 

16.9 
14.5 
16.0 


40.91 

47.95 
45.71 
42.79 


40.91 




Feb. 24, 1882 


48.91 


| 


" 28, " 


45.48 


ITT J 


Mch. 1, " 


43.22 


1 


Average 




I 


19.20 

18.20 
17.20 


15.8 

13.9 
16.6 


45.48 

50.72 
41.54 


45.87 


f 


Jan. 12, 1880... 


50.11 


TV J 


" 14, " 


42.29 


IV A 


Dec. 21, 1881 




{ 


17.70 

9.05 

8.83 

8.68 

8.53 

11.11 

10.87 


15.3 

19.2 

20.9 
20.2 
21.0 
18.4 
20.0 


46.13 

66.32 

60.28 
64.88 
60.66 
61.16 
57.86 


46.20 
69.10 




" 22, " 


64.19 




" 23, " 


68.58 




" 24, " 


64.66 


V J 


May 2, 1882 


63.42 




3, " 


61.04 




Average 






9.51 

6.84 
6.36 
6.14 
6.83 
6.69 
6.56 
6.40 
6.66 
6.50 
6.36 
6.21 
6.15 
5.98 


19.95 

15.8 
23.6 
20.7 
18.2 
18.0 
15.0 
16.5 
14.6 
16.4 
16.3 
15.9 
18.4 
19.2 


61.86 

65.01 
63.65 
58.13 
71.07 
76.85 
71.60 
75.03 
61.55 
54.91 
53.64 
52.57 
61.06 
54.24 


65.16 


c 


Dec. 5, 1881 


65.77 




" 6, " 


69.70 




" 9, " 


61.79 




Feb. 1, 1882 


73.56 




2, " 


79.39 




3. " 


71.60 




4, " 


76.23 


VI J 


Jan 27, 1883 


61.11 




" 28. " 


55.73 




" 29, " 


54.39 




Feb. 2, " 


53.09 




" 10, " 


63.22 




" 11, " 


56.73 




Average 






6.44 

3.34 
3.05 
2.91 


17.6 

15.0 
12.7 
20.6 


63.02 

84.45 
97.86 
80.00 


64.79 


c 


Jan 30, 1880 


84.45 




Feb. 1, " 


95.41 


vii 4 


3, " 


84.88 


1 


Average 




I 


3.10 


16.1 


87.44 


88.25 









INTERNAL WORK. 
SUMMARY. 



361 





Average Live 

Weight, 
Kgs. 


Heat Production per Kg. 


Relative Heat 


No. of 
Animal. 


Observed, 
Cals. 


Corrected 

to 15°, 

Cals. 


Production 

(Corrected), 

Cals. 


I 


30.66 

23.71 

19.20 

17.70 

9.51 

6.44 

3.10 


36.18 
40.91 
45.48 
46.13 
61.86 
63.02 
87.44 


36.66 
40.91 
45.87 
46.20 
65.16 
64.79 
88.25 


100 


II 


112 


Ill 


125 


IV 


126 


V 


178 


VI 


177 


VII 


241 



Rubner also determined approximately the surface exposed by 
his animals, in part by direct measurement and in part by calcu- 
lation, and computed the heat production per square meter of sur- 
face, with the following results : 



No. of Animal. 


Surface, 
Sq. Cm. 


Heat 
Production per 
Square Meter, 

Cals. 


I 


10750 
8805 
7500 
7662 
5286 
3724 
2423 


1046 
1112 
1207 
1097 
1183 
1120 
1214 


II 


Ill 


IV 

V 


VI 


VII 





He also cites * the results of experiments by Senator on the heat 
production of fasting dogs, and a respiration experiment by Reg- 
nault & Reiset, as follows: 





Live Weight, 
Kgs. 


Calculated 
Surface, 
Sq. Cm. 

) 


Heat Production. 


No. 


Per Kg. 

Live Weight, 

Cals. 


Per Square 
Meter of Sur- 
face, Cals. 


VIII 

IX 

X 

XI 

XII 


10.80 
7.52 
6.09 
5.68 
5.40 
4.24 
5.59 


5423 
4285 
3722 
3534 
3462 
2924 
3508 


52.31 
53.76 
63.04 
68.40 
74.16 
69.12 
72.82 


1035 
944 
1031 
1101 
1157 


XIII 

XIV 


1003 
1154 







* Loc. cit., p. 551. 



362 



PRINCIPLES OF ANIMAL NUTRITION. 



With one exception, the results per square meter agree very well 
with those of Rubner, both absolutely and relatively. 

Rubner has also shown in later experiments * that the same 
thing is substantially true of guinea-pigs, both at zero and at the 
temperature of about 30 degrees, at which the heat production is at 
its mimimum (critical temperature). He likewise points outf 
that the well-known rapid metabolism of children as compared 
with adults is, so far as the available data show, quite closely pro- 
portional to their relative surface, and observations on the diet of 
a dwarf I gave a like result. 

Richet,§ working with an air-calorimeter of constant pressure, 
in which the heat production was measured by the amount of 
water displaced by the expansion of the air, obtained the following 
results on rabbits, and similar results upon guinea-pigs are also 
reported : 



Number of 
Experiments. 


Live Weight, 
Kgs. 


Heat 

per Kg., 

Cals. 


Total Heat 
Expressed in 
c.c. of Water 

Displaced. 


The Same 

per Unit of 

Surface. 


5 

10 


2.0-2.2 
2.2-2.4 
2.4-2.6 
2.6-2.8 
2.8-3.0 
3.0-3.2 


4.730 
3.985 
3.820 
3.650 
3.570 
3.320 


119 
110 
115 
119 
125 
130 


130 


12 

4 

6 


129 
127 

128 


7 


127 







It would appear from the description of the experiments that 
only the heat given off by radiation and conduction was measured, 
no specific statements being made as to ventilation or as to the loss 
of heat as latent heat of water-vapor. The experiments were also of 
short duration, ranging from sixty to ninety minutes. 

The same author in later experiments || determined the respi- 
ratory exchange^ of rabbits of different weights. Computing the 

* Biologische Gesetze, pp. 17-18. 

f Zeit. f. Biol., 21, 390. 

% Biologische Gesetze, p. 9. 

§ Archives de Physiol , 1885, II, 237. 

\\Ibid., 1890, pp. 17 and 483; 1891, p. 74; Comptes rend, 109, 190. 

Tf By means of an apparatus described briefly in Comptes rend., 104, 435 



INTERNAL WORK. 



3 6 3 



results per square centimeter of surface by the use of Meeh's for- 
mula (p. 364) he obtained the following figures, while similar 
results are also reported on guinea-pigs, rats, and birds. 



Number of 
Experiments. 


Average Live 
Weight, Kgs. 


Carbon Dioxide 

per Square Cm. 

of Surface, 

Mgrs. 


4 


24.0 
13.5 
11.5 
9.0 
6.5 
5.0 
3.1 
2.35 


2.65 
2.60 
2.81 
2.81 
2.69 
2.57 
2.71 
2.70 


5 

7 

4 

3 

3 

6 

4 



E. Voit * has recently published an extended compilation of 
results bearing upon this point, including experiments on man, dogs, 
rabbits, swine, geese, and hens, the heat production being in most 
cases computed from the metabolism of carbon and nitrogen. The 
results when computed per square meter of surface, while they 
show not inconsiderable variations in some individual cases, never- 
theless as a whole substantially confirm the conclusion that the 
fasting metabolism is in general proportional to the surface. Still 
more recently Oppenheimer f has shown that the law also holds 
good for infants. 

Causes of Variations. — In comparing experiments made upon 
different animals by different observers at different times some 
variation in the results would naturally be expected. The experi- 
ments compiled by Voit were not all made at the same temperature, 
but the range in most cases is relatively small and can hardly have 
exerted any considerable influence. Differences between the differ- 
ent animals as to their normal rate of emission of heat (thickness of 
coat, quality of skin) may perhaps have also had an effect, although 
probably a small one. 

A more important source of error seems to lie, as Voit points 
out, in the computation of the results to unit surface, what is 
actually measured, of course, being the total heat production of 
the animal. In solids which are of the same shape, that is, which 



*Zeit. f. Biol., 41, 113. 



t Ibid., 42, 147. 



364 PRINCIPLES OF ANIMAL NUTRITION. 

are geometrically similar figures, the surface is proportional to 
the two-thirds power of the volume. If we let S = surface and 
V = volume, then S = kV*, in which k is a constant for any given 
form. Putting W = weight, if the bodies have the same specific 
gravity we may substitute W for V in the above equation, and we 
then have 

S = kW*, k = ~. 

On the assumption that the bodies of animals of the same species 
constitute similar figures and have the same specific gravity, the 
value of k has been determined for several species, as follows (the 
weight being expressed in kilograms and the surface in square 
centimeters) : 

Man 12.9 Meeh (Zeit. f. Biol., 15, 425). 

Dog 11.2 Rubner {Ibid., 19, 548). 

Rabbit 12.9 Rubner {Ibid., 19, 553). 

Horse 9.02 Hecker (Zeit. f. Veterinark., 1894). 

Hen 10.45 Rubner (Zeit. f. Biol., 19, 553). 

Guinea-pig .... 8.89 Rubner (Biol. Gesetze, p. 17). 

Rat 9.13 ) ■ ,„ . 

Fro 4 62 \ Rubner (Zeit. f. Biol., 19, 553). 

The heat production per unit of surface in most of the foregoing 
experiments is computed by the use of these factors. The results 
of such computations, however, are necessarily approximations 
only. While animals of the same species are of the same general 
shape, we can by no means regard them as being exactly similar 
figures in the geometrical sense, nor can we safely assume them to 
be of exactly the same specific gravity, since changes in the 
amount of contents of stomach and intestines, and particularly in 
the quantity of fat in the body, would cause greater or less variations. 
Moreover, the state of fatness has, as Voit points out, still another 
effect. As an animal grows fat, the increase in size is mainly 
transverse and not longitudinal, the effect being like that of in- 
creasing the diameter of a cylinder of fixed length.* In such a 
case, however, the increase in the surface is not proportional to the 
two-thirds power of the volume, nor to the square root of the vol- 

* In the case of an animal, of course, we have the additional fact that the 
deposit of fat is not of uniform thickness over the whole surface of the body. 



INTERNAL WORK. 365 

ume, as Voit states. The curved surface of the cylinder will be 
proportional to the square root of its volume, while the surface of 
the two ends will be proportional to the volume, and the ratio of 
total surface to volume will depend upon the ratio of length to 
diameter, being greater as the latter becomes less. 

Obviously, the calculation of the surface of an animal from its 
weight is a more or less uncertain one, and it is not surprising that 
the results should be somewhat fluctuating. It seems very doubt- 
ful, however, whether the larger differences found in Voit's com- 
pilation can be explained in this way, and Voit shows that there 
is another factor to be considered, viz., the mass of active cells in 
the body, which has a material bearing on the results. Before 
proceeding to a discussion of this point, however, it is desirable to 
consider briefly the significance of the general fact of the close 
relation between heat production and surface. 

Significance of Results. — Let us imagine an animal exposed to 
its "critical thermal environment" (p. 358) to gradually shrink in 
size while the external conditions remain the same. Under such 
circumstances the loss of heat to its surroundings will tend to in- 
crease relatively to its mass — that is, the body, like an inanimate 
object, will tend to cool more rapidly. This tendency can be met 
and the body temperature maintained in only two ways, viz., either 
by some modification of its surface — e.g., thicker hair — which will 
lower what we may call its emission constant, or by a relative in- 
crease in its rate of heat production. 

The results which we have been considering show that in 
general the emission constant, i.e. the rate of heat emission per 
unit of surface, is substantially the same in small and large animals, 
and that the greater loss of heat in the former case is met by an 
increased production. In this aspect the effect is simply an ex- 
tension of the influence of falling temperature, the increased de- 
mand for heat being met by an increased supply, so that the extent 
of surface appears as the determining factor of the amount of met- 
abolism. 

In the case of an animal exposed to a temperature below the 
critical point, however, the increased demand for heat appears to be 
met largely by a stimulation of those processes of metabolism which 
do not result in any visible form of work, while the internal work, 



3 66 



PRINCIPLES OF ANIMAL NUTRITION. 



in the more restricted sense of the ordinary functions of the internal 
organs, does not seem to be materially affected. Are we justified 
in assuming the same thing to be true in our imagined shrinkage 
of an animal? In other words, is the work of the internal organs 
proportional to the mass of the body and is the increased heat 
production in the smaller animal due to the same cause as that 
observed when an animal is exposed to a falling temperature? 

It appears quite clear that this question must be answered in 
the negative. It is a well-known fact that the circulation, respira- 
tion, and other functions are as a rule more active in small 
than in large animals, and this greater activity must necessarily 
result in the evolution of relatively more heat. If we raise the 
temperature of the surroundings to a point corresponding to the 
critical thermal environment, we may, as we have seen, regard the 
heat production as representing the internal work in the narrower 
sense. Rubner * reports experiments of this sort upon four guinea- 
pigs at 0° C. and at 30° C, which gave the following results for the 
production of carbon dioxide : 



Weight of 


C0 2 per Hour at 0° C. 


C0 2 per Hour at 30° C. 


Animal, 

Grms. 


Per Kg. 

Weight, 

Grms. 


Per Square 

Meter Surface, 

Grms. 


Per Kg. 

Weight, 

Grms. 


Per Square 

Meter Surface, 

Grms. 


617 
568 
223 
206 


2.905 
3.249 
4.462 
4.738 


27.85 
30.30 
30.47 
31.56 


1.289 
1.129 

1.778 
1.961 


12.35 
10.53 
12.14 
13.16 



With the first and third of these animals direct experiment 
showed that the minimum production of carbon dioxide (critical 
point) was reached at about 30°-35°, and we may fairly assume 
this to be true of the other two. At 30° C, then, we may assume 
that the " chemical " regulation was practically eliminated and that 
the observed metabolism was that due to the work of the internal 
organs. Under these conditions, as the figures show, the metab- 
olism was still approximately proportional to the surface of the 
animal, and consequently greater per unit of weight in the smaller 
than in the larger animals. 

* Biologische Gesetze, pp. 12-18. 



INTERNAL WORK. 367 

Strong confirmation of this conclusion is afforded by the exper- 
iments previously cited. In many of them, notably in Rubner's, 
the range of size is so great that to regard the differences in heat 
production as arising from a direct stimulation of the metab- 
olism, as in the case of a fall in the external temperature, leads 
to improbable consequences. Thus a comparison of the largest 
with the smallest dog in Rubner's experiments (p. 361) shows 
that if we regard the heat production of the former as represent- 
ing simply the work of the internal organs, over 56 per cent, of the 
heat production of the smaller animal must, on the supposition 
that the internal work is proportional to the mass of the body, have 
arisen from some other source. Such an enormous increase in the 
metabolism of the body simply for the sake of heat production 
can hardly be regarded as probable. Still further, if we assume 
(compare p. 354) a temperature of about 20° C. to represent the 
critical point for the dog, then, on the hypothesis that the necessary 
internal work per unit of weight is the same, we find that a fall of one 
degree in temperature must have produced about six times the 
effect upon the metabolism of the smallest dog that it did on that 
of the largest one, while if we take the other alternative and seek to 
explain the results on the assumption of a higher critical tempera- 
ture for the smallest dog, we find for the latter about 36^° C. 

Taking these considerations along with the results of Rubner's 
trials with the four guinea-pigs, it seems most reasonable to assume, 
in default of more extensive investigations directed to this specific 
point, that the critical temperature is substantially the same for 
large and small animals of the same species and that the work of 
the internal organs is approximately proportional to the surface 
of the animal. 

Substantially the same conclusion has been reached by v. Hoss- 
lin * from a quite different point of view. He points out that the 
increased production of heat below the critical temperature is not 
proportional to the difference in temperature between the body and 
its surroundings, as it should be, according to Newton's law, if the 
emission constant of the surface remained the same. Taking as an 
example Theodor's experiments (p. 351) he makes the following 
comparisons : 

* Arch. f. (Anat. u.) Physiol., 1888, p. 323. 



3 68 



PRINCIPLES OF ANIMAL NUTRITION. 



External 
Temperature, 


Difference Between Body and 
External Temperature. 


Carbon Dioxide in 12 Hours. 


Degrees. 


Total, 
Degrees. 


Relative. 


Total, 
Grms. 


Relative. 


30.8 

20.1 

12.3 

0.2 

-5.5 


7.2 

17.9 
25.7 
37.8 
43.5 


1.0 

2.5 

3.6 

5.25 

6.0 


12.03 
14.34 
17.76 
18.24 
19.83 


1.00 
1.19 
1.48 
1.52 
1.65 



It would appear from these figures that even below the critical 
temperature the "physical" regulation plays a large part in the 
regulation of the body temperature, being simply supplemented 
by the "chemical" regulation, and that therefore the demand for 
heat has not the determining influence upon the heat production 
which Rubner supposes. According to v. Hosslin the apparent 
dependence of the total metabolism upon the surface is only a par- 
ticular case of a general morphological law and he points out: 

First, that since, according to him, the velocity of the circula- 
tion does not vary greatly in large and small animals, the average 
amount of blood passing through the organs, and consequently 
their supply of oxygen, will be proportional to the total cross- 
section of the blood-vessels, which again, similar form being 
assumed, will be proportional to the two-thirds power of the 
volume (or weight) of the body. 

Second, that the capacity of the alimentary canal to digest and 
resorb food and thus to supply material for metabolism is limited 
in the same proportion. 

Third, that the work of locomotion — substantially the only 
form of external work in the wild state — at a given speed is pro- 
portional to the two-thirds power of the weight. 

In short, v. Hosslin claims that all the important physiological 
activities of the body, including, of course, its internal work and the 
consequent heat production, are substantially proportional to the 
two-thirds power of its volume, and that since the external surface 
bears the same ratio to the volume, a proportionality necessarily 
exists between heat production and surface. According to this 
view, then, the heat production of the fasting animal at the criti- 
cal temperature represents the internal work, which is proportional 



INTERNAL WORK. 



3 6 9 



to the two-thirds power of the volume of the body, while below 
this point there is superadded a stimulating effect upon the heat 
production, which, since it acts through the surface, we may 
assume to be proportional to the latter. 

Comparison of Species. — In the foregoing discussion compari- 
sons have been made between large and small animals of the same 
species, with the result that both their internal work and their 
total fasting metabolism appear to be closely proportional to their 
surface. Going a step further and comparing the average results 
of the several species with each other, E. Voit * reaches the inter- 
esting and striking result that the same relation of total fasting 
metabolism to surface is substantially true as between different 
species. The following table contains the averages, with the addi- 
tion of the fasting metabolism of the horse as computed by Zuntz 
& Hagemann, which Voit believes with good reason to be too 
low: 





Average Tem- 
perature, 
Deg. C. 


Average 
Weight. Kgs. 


Fasting Metabolism. 




Per Kg., 
Cals. 


Per Square 
Meter, Cals. 


Horse 

Swine 

Man 


9.1 (?) 
20.1 
14.3 
18.0 
18.2 
15.0 
18.5 


441 

128 

64.3 

15.2 

2.3 

3.5 

2.0 


11.3 
19.1 
32.1 
51.5 
75.1 
66.7 
71.0 


>948 
1078 
1042 


Dog 


1039 


Rabbit 

Goose 

Hen 


776 
967 
943 



With the exception of the rabbit, the average heat production 
of these various animals per unit of surface does not show any 
greater variations than have been observed between different 
animals of the same species, more or less of which, as we have seen, 
can probably be accounted for by errors in the estimate of the 
surface of the body. 

Accepting the fact of the general proportionality of heat pro- 
duction to surface, and passing over for the moment the excep- 
tional case of the rabbit, it is plain that the considerations which 
have been adduced in discussing the results upon the same 

* Loc tit., p. 120. 



37° PRINCIPLES OF ANIMAL NUTRITION. 

species will in the main apply to a comparison of different species. 
It is true that what data we have indicate that there may be more 
or less difference between the critical temperatures for different 
species, but in view of the enormous range in the size of the animals 
experimented on this cannot largely modify the results. Any 
reasonable assumptions as to critical temperatures and as to rates 
of variation per degree in heat production would still leave the 
corrected results substantially proportional to the surface. Appar- 
ently we must conclude that in all these different species, as well 
as in larger and smaller animals of the same species, the internal 
work, as measured by the total metabolism at the critical tem- 
perature, is substantially proportional to the surface. 

How generally this may be true we have at present no means 
of judging. It is clear, however, that in the process of organic 
evolution one of the very important factors has been the demand 
for heat exerted by the environment upon the animal. This has 
been met to some extent by modifications in the coat of the animal, 
but to a very large degree by changes in the rate of heat produc- 
tion, with the result that, other things being equal, those forms have 
survived whose normal heat production, resulting from internal 
work alone, was sufficient to maintain their temperature under the 
average conditions surrounding them without, on the one hand, 
calling largely into play the processes of "chemical" regulation, 
nor, on the other hand, producing so much heat as to render it 
difficult for the body to get rid of it. 

Relation of Heat Production to Mass of Tissue. — As 
already indicated, E. Voit. in his article cited above, has shown 
that while the heat production is in general proportional to the sur- 
face, there is also another determining factor, viz., the mass of the 
active cells in the organism, a rough measure of which is the total 
nitrogen of the body exclusive of that of the bones and the skin. 
This conclusion is based chiefly on experiments with fasting animals. 
As the weight of such an animal decreases, its relative surface must 
increase, and, as was shown on p. 364, probably more rapidly than 
in proportion to the two-thirds power of the weight. Under these 
circumstances we should naturally expect that the relative heat 
production would increase, but as a matter of fact it rather shows 
a tendency to decrease. E. Voit, in discussing the results of Rubner 



INTERNAL WORK. 



371 



and others, computes the heat production per unit of surface, and 
also compares it with the amount of nitrogen computed to be 
present in the organs of the animal on the several days of the ex- 
periment. The following results of one of Rubner's experiments 
with rabbits are typical of those obtained in this way : 





Average 

Live 
Weight, 
Grms. 


Heat Production per Day. 


Day of Fasting. 


Total, 

Cals. 


Per Kg.. 

Cals. 


Per 

Square 

Meter of 

Surface, 

Cals. 


Per 100 

Nitrogen, 
Cals. 


Third 


2185 
2093 
2007 
1923 
1841 
1735 
1646 
1507 


155 

117 

102 

97 

95 

88 
81 
72 


71.0 
55.9 
50.8 
50.5 
51.6 
50.7 
49.2 
47.8 


730 
556 

499 
488 
494 
463 
452 
428 


310 


Fifth 


243 


Seventh 


220 


Ninth 


221 


Tenth and twelfth 


227 


Thirteenth and fourteenth . . 
Fifteenth and sixteenth .... 
Seventeenth and eighteenth 


222 
218 
219 



The heat production per unit of surface is seen to decrease at 
first rapidly and later more slowly, while the heat production per 
unit of weight shows but a slight decrease and that per unit of 
nitrogen scarcely any. From these and other similar results, Voit 
concludes that the law of the proportionality of heat production to 
surface as enunciated by Rubner and as extended by himself must 
be limited in its application to animals in like bodily condition, 
and that an animal with a low stock of nitrogenous tissue will, 
under the same conditions, show a lower heat production per unit 
of surface than a well-nourished animal. The exceptionally low 
average for the rabbit noted on p. 369 he explains on this hypoth- 
esis as resulting from the frequent use for such experiments of 
animals in a poorly nourished and "degenerate" condition re- 
sulting from long confinement. 

The result has an interesting bearing in another direction. 
Most of the experiments cited by Voit were probably made at tem- 
peratures below the critical points for the several animals. In 
our previous discussion we have assumed that under these circum- 
stances the heat regulation is accomplished largely by " chemical " 
means — by variations in the rate of production. In these experi- 



37 2 



PRINCIPLES OF ANIMAL NUTRITION. 



merits, on the contrary, since the heat production decreased along 
with the decrease of nitrogenous tissue, we see the regulation of 
body temperature effected by a diminution in the rate of emission 
of heat, which, however, was in most cases less marked than in the 
instance just cited. Either we must conclude that the abnormal 
condition arising from fasting enables the animal to diminish the 
rate of emission of heat to an extent not possible to the well- 
nourished one, or we may suppose that in the latter case the stimu- 
lation of the metabolism by the abstraction of heat begins before 
the possibilities of "physical" regulation have been exhausted; 
that, in other words, the domains of "chemical" and "physical" 
regulation overlap. Obviously the latter conclusion is entirely in 
harmony with v. Hosslin's views as stated on pp. 367-8. 



§ 3. The Expenditure of Energy in Digestion and Assimilation. 

General Conception. 

Food Increases Metabolism. — That the consumption of food 
increases the metabolism and consequent heat production in the 
body has been known since the time of Lavoisier, who observed 
the oxygen consumption of man to increase materially (about 37 
per cent.) after a meal. Regnault & Reiset * also, among their 
respiration experiments on animals, report the following results 
for the oxygen consumption of two rabbits while fasting and after 
eating : 



Animal. 


Easting, 
Grms. 


After Eating, 
Grms. 


A 


2.518 
2.731 


3.124 
3.590 


B 





Subsequent investigations by Vierodt, Smith, Speck, Fredericq, 
v. Mehring & Zuntz, Wolfers, Potthast, Hanriot & Richet,f Magnus- 
Levy, Zuntz & Hagemann, Laulanie, and others, some of which will 
be considered more specifically in subsequent paragraphs, have fully 
confirmed these earlier results, so that the fact of an increased met- 
abolism consequent upon the ingestion of food is undisputed. 

* Ann. de Chim. et de Phys. (3), 26, 414. 

f Ibid. (6), 22, 520. 



INTERNAL WORK. 373 

Cause of the Increase. — Two possible explanations of the 
above fact naturally suggest themselves, viz., that, on the one hand, 
the more abundant supply of food material to the cells of the 
body may act as a direct stimulus to the metabolic processes, or, 
on the other hand, that the increased metabolism may arise from 
the greater activity of the organs of digestion, or finally, that both 
causes may act simultaneously. 

The results obtained by Speck,* who found that the increase 
began very promptly (within thirty minutes) after a meal, would 
indicate that it can hardly be due to a stimulating action of the 
resorbed food upon the general metabolism, but must arise, in 
large part at least, from the activity of the digestive organs. 
Specific investigations upon this point were undertaken by Zuntz & 
v. Mehring.f They found that glycerin, sugar, egg-albumin, puri- 
fied peptones, and the sodium salts of lactic and butyric acids \ 
when injected into the circulation caused no material increase in 
the amount of oxygen consumed as determined in successive short 
periods by the Zuntz form of respiration apparatus. It is well estab- 
lished that some of these substances do increase the metabolism 
when given by the mouth, and the authors verified this fact for sugar 
and for sodium lactate and likewise showed that substances like 
sodium sulphate, which are not metabolized in the body, caused a 
similar rise in the metabolism when introduced into the digestive 
tract. They therefore conclude that the effect of the ingestion of 
food upon the metabolism is due chiefly to the expenditure of energy 
required in its digestion. Wolfers § andPotthast,|| in experiments sup- 
plementary to those just mentioned, obtained confirmatory results. 

On the other hand, Laulanie,^[ in the experiments mentioned 
on p. 180 in their bearings upon the formation of fat from carbo- 
hydrates, obtained almost as marked an increase in the oxygen 
consumption subsequent to the injection of sugar into the circula- 
tion as after its administration by the mouth. 

* Arch, exper. Pathol, and Pharm., II, 1874, p. 405. 
t Arch. ges. Physiol., 15, 634; 32, 173. 

% The results of their experiments upon organic acids have already been 
cited in Chapter V, p. 157, in another connection. 
§ Arch. ges. Physiol., 32, 222. 
|| Ibid., 32, 280. 
\ Archives de Physiol., 1896, p. 791. 



374 PRINCIPLES OF ANIMAL NUTRITION. 

On the whole, however, and in view of the patent fact that the 
activity of the digestive apparatus consequent upon the consump- 
tion of food must lead to an expenditure of energy, the results of 
Zuntz & v. Mehring appear to have been generally accepted as proof 
that it is this influence rather than any direct effect of the resorbed 
food upon the metabolism to which the increase of the latter after 
a meal is to be ascribed. This increased expenditure is often, 
although rather loosely, spoken of as the "work of digestion." 

Factors of Work of Digestion. — In the process of digestion 
we are probably safe in assuming that the muscular work of pre- 
hension, mastication, deglutition, rumination, peristalsis, etc., con- 
stitutes an important source of heat production. A secondary 
source of heat production, which we may designate as glandular 
metabolism, is the activity of the various secretory glands which 
provide the digestive juices, to which may be added also the work 
of the resorptive mechanisms. Furthermore, the various processes 
of solution, hydration, cleavage, etc., which the nutrients undergo 
during digestion contribute their share to the general thermic effect. 

Fermentations. — To the above general sources of heat produc- 
tion during the digestive process, there is to be added as a very 
important one in the case of ruminating animals the extensive fer- 
mentation which the carbohydrates of the food undergo. We have 
already seen that a considerable fraction of the gross energy of these 
bodies is carried off in the potential form in the combustible gases 
produced. A further portion is liberated as heat of fermentation. 
This latter portion forms a part of the metabolizable energy of the 
food as defined in the preceding chapter, since it assumes the kinetic 
form in the body. Since, however, it appears immediately as heat, 
it can be of use to the body only indirectly, as an aid in maintaining 
its temperature. While, therefore, it does not constitute work in 
the strict sense of the term, the heat produced by fermentation 
constitutes a part of the expenditure of metabolizable energy in 
digestion, and therefore is included under the term " work of diges- 
tion " in the general sense in which the term is frequently used. 

Warming Ingesta. — The food, and particularly the water, con- 
sumed by an animal have to be warmed to the temperature of the 
body. To the extent that this warming of the ingesta is accom- 
plished at the expense of the heat generated by the muscular, gland- 



INTERNAL WORK. 375 

ular, and fermentative actions indicated above, it does not call for 
any additional expenditure of energy and so does not, from the 
statistical point of view, constitute part of the "work of digestion." 
If, however, at any time the warming of the ingesta requires more 
heat than is produced by these processes — if, for example, a large 
amount of very cold water is consumed — it is evident that the 
surplus energy required will be withdrawn from the stock otherwise 
available for other purposes, and to this extent will increase the 
expenditure of energy consequent upon digestion. 

The Expenditure of Energy in Assimilation. — While our 
knowledge of the changes which the nutrients undergo after re- 
sorption is very meager, we may regard it as highly probable that 
they undergo important transformations before they are fitted to 
serve directly as sources of energy for those general vital activities 
of the body represented in gross by the fasting metabolism. 

Thus the proteoses and peptones produced in the course of 
digestive proteolysis are synthesized again to proteids, while the 
proteids, when the supply is large, undergo, as was shown in Chap- 
ter V, rapid nitrogen cleavage, leaving a non-nitrogenous residue 
as a source of energy. According to some authorities, as we have 
seen, the resorbed fat undergoes conversion into dextrose in the 
liver before entering into the general metabolism of the body. 
Even the carbohydrates, at least so far as they are not directly 
resorbed as dextrose, seem to undergo more or less transformation 
before entering into the general circulation. 

In brief, there seems good reason to believe that the crude mate- 
rials resulting from the digestion of the food undergo more or less 
extensive chemical transformations before they are ready to serve 
as what Chauveau calls the "potential" of the body — that is, as 
the immediate source of energy for the vital functions. Of the 
nature and extent of these transformations we are largely ignorant. 
So far as they are katabolic in their nature, a liberation of energy is 
necessarily involved. Any anabolic processes of course would 
absorb energy, but the energy so absorbed must come ultimately 
from the katabolism of other matter, and in all probability there 
would be more or less escape of kinetic energy in the process. 

Moreover, as was pointed out in the opening paragraphs of 
Chapter II in discussing the general nature of metabolism, as well 



376 PRINCIPLES OF ANIMAL NUTRITION. 

as in the Introduction, the vital activities are intimately connected 
with the katabolic processes going on in the protoplasm of the 
cells. As was there stated, it is highly probable that the molecules 
of the protoplasm are much more complex than those of the pro- 
teids, fat and carbohydrates of the food (compare pp. 17 and 224). 
To what extent it is necessary that the resorbed nutrients shall be 
synthesized to these more complex compounds before they can 
serve the purposes of the organism we are hardly in position to 
say, but so far as it is required it can be accomplished only by an 
expenditure of energy derived ultimately from the food and con- 
stituting a part, and not impossibly a large part, of the work of 
assimilation. 

Summary. — The considerations of the foregoing paragraphs 
make it plain that the exercise of the function of nutrition, as is the 
case with the other functions of the body, involves the expenditure 
of energy. In general, we may say that this energy is expended for 
the two purposes indicated in the title of this section, viz., for diges- 
tion, or the transformation of the crude materials of the food and 
their transference to the fluids of the body, and for assimilation, or 
the conversion of these resorbed materials into the " potential " of 
the organism. Each of these two general purposes is served by a va- 
riety of processes, and the attempt to assign to each its exact share 
in the increased metabolism brought about by the ingestion of food 
is a physiological problem at once interesting and complicated. 

For our present purpose, however, viz., a consideration from the 
statistical point of view of the income and expenditure of energy 
by the organism, we are concerned primarily with the total ex- 
penditure caused by the ingestion of food rather than with the 
single factors composing it. As a matter of convenience it may be 
permissible to retain the designation above given, viz., the work of 
digestion and assimilation, but it should not be forgotten that other 
processes may conceivably be concerned in the matter. In par- 
ticular, any increased heat production resulting from a direct stimu- 
lation of the metabolic processes or of the incidental muscular 
activity of the animal by the resorbed food, such for example, as 
Zuntz & Hagemann * have observed with the horse as a result of 
abundant feeding, particularly with Indian corn, would be included 
under the term as here used. 

* Landw. Jahrb., 27, Supp. Ill, 234 and 259. 



INTERNAL WORK. 377 

Experimental Results. 

General Methods. — It follows from what has been said above 
that two general methods, or more properly two modifications of 
one general method, may be employed to determine the total ex- 
penditure of energy due to the ingestion of food. 

First, since the energy expended in the various processes out- 
lined above is ultimately converted into heat, we may determine the 
heat production of the animal while fasting and compare with it the 
heat production during the digestion and assimilation of a known 
amount of food. The excess of heat produced in the latter case as 
compared with the former will represent the increased expendi- 
ture of energy in the work of digestion and assimilation. 

Second, we may determine the total income and outgo of energy 
in the fasting and in the fed animal by one of the methods indicated 
in Chapter VIII. In this case the extent to which the net loss of 
energy by the body has been diminished by means of the food will 
show how much of the metabolizable energy of the latter has been 
utilized by the organism in place of that previously drawn from the 
metabolism of tissue. The part of the metabolizable energy not 
thus utilized has obviously been expended in some of the various 
operations of digestion, assimilation, etc. The two methods are com- 
plementary, in the one case the expenditure for digestion, assimila- 
tion, etc., being determined directly and in the other by difference. 

A point of some importance, at least logically, is that the deter- 
minations should be made below the point of maintenance. The 
term assimilation as above defined includes all those processes by 
which the resorbed nutrients are prepared for their final metabo- 
lism in the performance of the vital functions. When we give food 
in excess of the maintenance requirement, however, there is added 
to this the set of processes by which the excess food is converted 
into suitable forms for more or less temporary storage in the 
body. These may be presumed to consume energy, and as it would 
seem, to a more or less variable extent. At any rate, we have 
no right to assume in advance that the relative expenditure of en- 
ergy above the maintenance point in the storage of excess material 
is the same as that below the maintenance point for the processes 
of assimilation as above defined. In other words, it is not necessa- 
rily nor even, it would seem, probably the case that the resorbed 



37 8 PRINCIPLES OF ANIMAL NUTRITION. 

portion of a maintenance ration is first converted into the same 
materials (particularly fat) that are deposited in the body when 
excess food is given, and that these materials are then metabolized 
in the performance of the bodily functions. It is at least conceiv- 
able, if not likely, that a much less profound transformation, and 
one involving a smaller loss of energy, suffices to prepare the re- 
sorbed nutrients for their functions as " potential " than is required 
for their storage as gain of tissue. 

Finally, the comparison need not necessarily be made, and in- 
deed in case of most agricultural animals cannot well be made, with 
the fasting state. While this method is the simpler when practi- 
cable, a comparison of the total heat production or of the balance 
of energy on two different rations (both being less than the mainte- 
nance requirement) will afford the data for a computation by differ- 
ence (exactly similar to that employed in the determination of 
metabolizable energy in Chapter X) of the expenditure of energy in 
the digestion and assimilation of the food added to the basal ration. 

The most important quantitative investigations upon the work 
of digestion are those of Magnus-Levy * on the dog and on man, 
and those of Zuntz & Hagemann f upon the horse. 

Experiments on the Dog. — In Magnus-Levy's experiments 
the respiratory exchange of the animal was determined by means 
of the Zuntz apparatus at intervals of one or two hours during 
fasting and after feeding. The single periods were twenty-five to 
thirty minutes long, and the external conditions were maintained 
as uniform as possible. 

Fat. — Fat (in the form of bacon free from visible lean meat), 
when given in quantities not materially exceeding in heat value 
the fasting metabolism, resulted in a slight increase of the latter, 
beginning about one to three hours after eating, reaching its maxi- 
mum between the fifth and ninth hours, and disappearing about the 
twelfth hour. The maximum increase observed was 12 per cent., 
seven hours after eating. In amounts largely exceeding the equiv- 
alent of the fasting metabolism the effect of fat was somewhat 
more marked and longer continued, a maximum increase of 19.5 
per cent, being observed in one case seven hours after eating, while 

* Arch. ges. Physiol., 55, 1. 
t Landw. Jahrb., 27, Supp. III. 



INTERNAL WORK. 



379 



the metabolism was still slightly above its fasting value after eight- 
een hours. The respiratory quotient in every case sank to a value 
closely corresponding to that for the oxidation of pure fat. 

The experiments do not permit an exact estimate of the total 
increase of the metabolism during the twenty-four hours, since 
the observations were not always made at hourly intervals and 
but few of the trials extended over a full day. By selecting, 
however, the two in which the data are most complete and com- 
puting as accurately as may be the average rate of consumption 
of oxygen per minute, it is possible to obtain an approximate 
expression for the total heat production. For this purpose the 
average oxygen per minute is multiplied by 1440 and this product 
by the calorific equivalent of the oxygen, viz., 3.27 Cals. per gram 
in this case, and the following results obtained, the heat production 
during fasting being in each instance that found in the particular 
experiment under consideration: 





Fat 
Eaten, 
Grms. 


Energy 

of Food, 

Cals. 


Heat Production in 24 Hours. 


No. of 
Experiment. 


Fasting, 
Cals. 


With 
Food, 
Cals. 


Increase. 




Cals. 


Per Cent, 
of Food. 


100 

64 and 68 


131.6 
305.5 


1250 
2902 


972 • 
1055 


991 
1142 


19 

87 


1.53 
2.99 



Carbohydrates. — Carbohydrates produced a more marked 
effect upon the metabolism than did fat, and one which showed 
itself more promptly. In the experiments on the dog the food 
consisted of rice, either alone or with the addition of small amounts 
of fat, sugar, or meat; in other words, the animal was on a mixed 
diet in which carbohydrates predominated. 

On the average of a series of six experiments in which the food 
consisted of 500 grams of rice, 200 grams of meat, and 25 grams of 
fat, the metabolism increased by fully 30 per cent, within the first 
hour and continued to increase more slowly until the maximum of 
39 per cent, was reached at the sixth to eighth hour. From that 
time it decreased to 25 per cent, in the twelfth hour and then rather 
suddenly dropped nearly to the fasting value. The respiratory 
quotient rose from 0.78 during fasting to 0.90 in the first hour, and 



3 8o 



PRINCIPLES OF ANIMAL NUTRITION. 



reached very nearly 1.00 by the third hour, remaining at substan- 
tially this value for sixteen to eighteen hours and not falling to the 
fasting value in twenty-four hours. Two parallel experiments in 
which 400 grams of meat were fed showed that a part, but by no 
means all, of the above increase was to be ascribed to the 200 grams 
of meat. The small amount of fat given can hardly have affected 
the result. The author estimates that of the total calculated in- 
crease of 22 per cent, over the fasting metabolism about 5 per 
cent, may have been due to the proteids of the food and the 
remainder to the carbohydrates. This conclusion is confirmed by 
the results of two experiments in which rice, sugar, and fat were 
given. The increase in the metabolism was of precisely the same 
character as in the other experiments, but less in amount. 

In all these experiments the food was in excess of the fasting 
metabolism. In another series in which the food, consisting of rice, 
either alone or with a small amount of sugar, was about equivalent 
to the fasting metabolism, the increase in the metabolism was 
slightly less, although otherwise the results were similar to those 
of the other trials. 

Computing the results per twenty-four hours, as in the case of the 
fat, we have the following approximate figures for the three series : 





Food* 
Grms. 


Metab- 
oliza- 

ble 
Energy 

of 

Food.t 

Cals. 


Heat Production in 24 Hours. 


No. of 
Experiment. 


Fast- 
ing, 
Cals. 


With 
Food, 
Cals. 


Increase. 


Cals. 


Per 

Cent, of 
Food. 


68, 70, ( 

71, 73, \ 

74, and 75 ( 

84 and 87 \ 

107 \ 


Proteids 71.3 | 

Carbohydrates.. 375.0 \ 
Fat 31.0 ) 

Proteids 28.1 ) 

Carbohydrates. . 457 . 5 r 
Fat 25.0 ) 

Proteids 18.75) 

Carbohydrates. . 225 . 00 \ 
Fat 1 


2121 

2226 

999 


1040 

1132 

991 


1271 

1292 
1080 


231 

160 

89 


10.89 
7.19 
8.91 



* Rice estimated to contain 75 per cent, carbohydrates and 1 per cent, 
nitrogen. 

f Computed by the writer, using Rubner's factors. 



INTERNAL WORK. 



38i 



Proteids. — Proteids in the form of meat or a mixture of meat 
and flesh-meal, with in some cases small amounts of fat, caused a 
very marked and prompt increase in the metabolism of the dog. 
The maximum effect was usually reached about the third or fourth 
hour and continued with but slight diminution up to the seventh 
or eighth hour with small rations and as long as to the twelfth or 
fifteenth hour with large rations. As in the case of fat and carbo- 
hydrates, the increase was greater with large rations, but its amount 
largely exceeded that caused by either of the two former groups of 
nutrients, reaching in some cases 90 or more per cent, of the fasting 
value. 

The results were more irregular than in the preceding experi- 
ments, and were apparently influenced by a peculiar effect of the 
food upon the type of respiration. The author, however,* com- 
putes from three selected series of experiments the following 
approximate averages for the twenty-four hours : 





Proteids 
Eaten, 
Grms. 


Metabo- 

lizable 

Energy 

of Food, 

Cals. 


[Heat Production in 24 Hours. 


No. of 
Experiment. 


Fasting, 
Cals. 


With 
Food, 
Cals. 


Increase. 




Cals. 


Per Cent, 
of Food. 


83 and 89 

102 " 106 

95 " 96 


82.5 
230.0 
370.6 


338 

943 

1520 


1030 

963 

1059 


1086 
1079 
1303 


56 
116 
244 


16.57 
12.30 
16.05 



The amount of the proteid metabolism was not determined in 
these experiments, but the author points out that they were made 
on the first day of the feeding, and that it is probable that the 
proteid metabolism, and consequently the heat production, would 
have increased more or less had the feeding, particularly with 
excess of food, been continued longer. 

Bone, when fed in large quantities to the dog, was found to 
cause a greater increase in the metabolism than corresponded to the 
nitrogenous matter estimated to have been resorbed from it, and 
the difference is ascribed to the mechanical effect upon the digestive 
tract. 

* Loc. cit., p. 78. 



382 



PRINCIPLES OF ANIMAL NUTRITION. 



Experiments on Man. — Magnus-Levy's experiments upon man 
were made substantially like those upon the dog, the subject lying 
upon a sofa, as completely at rest as possible, and breathing through 
a mouth-piece. 

Fat. — Two experiments with fat, computed in the same way as 
those upon the dog, gave the following results : 





Fat 
Eaten, 
Grms. 


Energy 

of Food, 

Cals. 


Heat Production in 24 Hours. 


No. of Experiment. 


Fasting, 
Cals. 


With 
Food, 
Cals. 


Increase. 




Cals. 


Per Cent, 
of Food. 


81 


94.0 
195.6 


893 
1855 


1537 
1524 


1547 
1582 


10 

58 


1.12 


21 


3.13 







Carbohydrates. — Numerous experiments on a man were made 
in which the diet consisted chiefly of bread, and a smaller number 
in which the effect of sugar was studied. With bread the increase 
in the metabolism was more prompt than in the experiments on the 
dog, but smaller in amount, varying from about 12 to as high as 33 
per cent., according to the amount eaten. By the end of the third 
hour the effect had nearly disappeared, but it was then followed 
by a second increase, less in amount but continuing longer, which 
the author suggests may have been due to the commencement of 
intestinal digestion. With sugar (both cane and grape) the increase 
was equally prompt, although rather less in amount, but dis- 
appeared entirely after two or three hours. None of the experi- 
ments extended over more than ten hours and usually over less, and 
the data given are insufficient for a satisfactory computation of the 
total increase for the twenty-four hours. The respiratory quotient 
was considerably raised, but did not reach 1.00 in any case. 

Proteids. — Experiments upon the effect of proteids on the 
respiratory exchange yielded results similar to those obtained with 
the dog, but do not permit of a satisfactory computation of averages 
for the twenty-four hours. 

Mixed Diet.— Results with a mixed diet the ingredients of 
which are not specified have been reported by Johansson, Lander- 



INTERNAL WORK. 



383 



gren, Sonden & Tigerstedt.* The experiments were made in a 
large Pettenkofer respiration apparatus and extended over twenty- 
two hours, the results being computed to twenty-four hours. The 
total heat production, as computed from the carbon and nitrogen 
balance, and the computed metabolizable energy of the food were.: 





Energy of Food, 
Cals. 


Heat Production, 
Cals. 


First day 


4141.4 
4277.9 










4355.9 
3946.4 


(?) 
2705.3 
2220.4 
2102.4 
2024.1 
1992.3 
1970.8 
2436.9 
2410.1 


Second " 


Third " 


Fourth " 


Fifth " 


Sixth " 


Seventh " 


Eighth " 


Ninth " 





The above figures furnish a striking example of the constancy of 
the fasting metabolism, and of the marked increase brought about 
by the consumption of food. Omitting the results for the first day 
of fasting and for the first day of the experiment we obtain the 
following averages: 

Average energy of food 4193 . 4 Gals. 

Metabolism ; 

With food 2517.4 " 

Fasting 2022.4 " 

Increase. 

Total 495.0 " 

Per cent, of food 11 . 76 Per cent. 

It is to be noted, however, that the food in this experiment was 
considerably in excess of the fasting requirements, so that there 
was a notable storage of material and energy in the body. 

Summary. — The results of the foregoing approximate computa- 
tions of the increased expenditure of energy for twenty-four hours 
are summarized in the following table, which also includes a com- 
parison of the metabolizable energy of the food with the fasting 
metabolism : 

* Skand. Arch. Physiol., 7, 29. 



384 



PRINCIPLES OF ANIMAL NUTRITION. 



Food. 


Metabolizable 
Energy of 
Food, Cals. 


Excess Above 

Fasting 

Metabolism, 

Cals. 


Digestive Work 
in Per Cent, 
of Metaboliz- 
able Energy. 


Fat: 

" dog.. S 


893 
1855 
1250 
2902 


-644 
+ 331 

+ 278 
+ 1847 


1.12 
3.13 
1.53 
2.99 








2.19 


Chiefly Carbohydrates : 

Experiments on dog .... J 


2121 

2226 

999 


+ 1081 
+ 1094 

+ 8 


10.89 
7.19 
8.91 








8.99 


Proteids : 


338 

943 

1520 


-692 

-20 

+ 461 


16.57 
12.30 
16.05 








14.97 


Mixed Diet : 

Experiments on man 


4193 


+2171 


11.76 







It is clear that proteids caused the greatest increase in the 
metabolism and fat the least, while the carbohydrates occupied an 
intermediate position. In the case of fat the increase in the heat 
production seems to show a slight tendency to become greater 
with amounts of food largely in excess of the fasting metabolism, 
but with the carbohydrates and proteids no distinct effect of this 
sort is apparent. 

These results, particularly those on proteids, afford a good illus- 
tration of the fact that the increase in the heat production caused 
by the ingestion of food is not due solely to the increased muscular 
work involved, since if we were to suppose the latter to be the case 
it is not apparent why the proteids, which are digested pretty 
promptly and with comparative ease, should cause seven times as 
much work as the fats. The results certainly suggest strongly that 
a large part of the heat production in the former case arises from 
the considerable chemical cleavage which the proteids undergo in 
digestion and still more from the stimulative effect of food proteids 



INTERNAL WORK. 3 8 5 

on the nitrogen cleavage ; in other words, that what was called 
on p. 375 the work of assimilation is an important factor. 

Results on Fat. — The relatively small increase in the metabo- 
lism resulting from the ingestion of fat is worthy of notice as bear- 
ing upon the hypothesis, already several times referred to, that it 
undergoes a cleavage into dextrose, carbon dioxide, and water in 
the liver, and that the resulting dextrose is the material which 
serves as the source of potential energy for the general metabolism. 
As was pointed out in Chapter V (p. 153), however, the dextrose 
derived from one gram of fat according to the commonly accepted 
equation would contain about 6.1 Cals. of potential energy out of 
the 915 Cals. contained in the original fat. In other words, over 
one third of the energy of the fat would be liberated as heat in the 
intermediary metabolism supposed to take place in the liver. 
While the heat production was not directly measured in Magnus- 
Levy's experiments, and while the method of computation em- 
ployed may be open to criticism in details, his results certainly fail 
to indicate any such large increase in the metabolism as this hypoth- 
esis would require. 

It should be noted, in conclusion, that the above experiments 
did not include a determination of the work of mastication and in- 
gestion of the food, and also that, according to the author, there 
was little if any production of fat in the experiments in which carbo- 
hydrates were fed. 

Experiments on the Horse. — Zuntz, Lehmann & Hagemann * 
have investigated the effect of digestive work and also of the masti- 
cation of the food on the metabolism of the horse, the respiratory 
exchange being determined by the Zuntz method and a correction 
made for the cutaneous and intestinal respiration. In addition to 
this, however, other data were secured which serve the authors as 
the basis for computations of the energy metabolism of the animal 
and of the available energy of the digested food. Since their most 
important conclusions as to digestive work are based in large part 
on the results of these computations it is necessary to consider 
their method in some detail. 

Method of Computation. — At six different times between the 

* Landw. Jahrb., 27, Supp., Ill, pp. 271-285. 



386 PRINCIPLES OF ANIMAL NUTRITION. 

years 1888 and 1891 digestion experiments were made * in which 
the total nitrogen metabolism | and the carbon of the food and of 
the visible excreta were determined. The ration in every case 
consisted of hay and a mixture of six parts of oats with one of cut 
straw; the chemical composition of these feeds was quite similar 
in the several experiments, the greatest variation being in the last 
experiment (October 16-22, 1891). 

From the results of these experiments the metabolism of 
energy in the respiration experiments is computed in the following 
manner : 

First, the results of the several digestion experiments are com- 
bined in such a way as to give an average corresponding to the ration 
during the respiration experiment. E.g., in Period 1 (loc. cit., p. 256) 
the ration consisted of 6 kgs. of oats, 1 kg. of straw, and 6 kgs. of 
hay. As no single digestion experiment was made on just this 
ration, the results of the first one are taken four times, those of the 
second three times, and those of the third once, and the sums divided 
by eight. These averages are taken as representing the digestibility 
and the urinary carbon and nitrogen during the respiration experi- 
ment. 

Second, from the average carbon and nitrogen of the urine as 
thus obtained its content of urea and hippuric acid is computed, 
and from these data, on the assumption of average composition for 
the metabolized proteids, the portion of the elements of the latter 
completely oxidized in the body, from which again the amount of 
oxygen required and of carbon dioxide produced is computed. 

Third, from the computed amount of crude fiber digested, 
assuming it to have the composition C 6 H 10 O 5 and that 100 grams 
yield 4.7 grams of methane, is computed the oxygen required for 
its oxidation and the carbon dioxide resulting. 

Fourth, after subtracting the amounts of oxygen and carbon 
dioxide, as above computed, corresponding to the proteids and 
crude fiber oxidized, from the totals found in the respiration experi- 
ment, the remainders are divided between fat and carbohydrates 

* Loc. cit., pp. 211-236. 

f The nitrogen of the feces was determined in the air-dried material. 
Subsequent experience has shown that there is some loss of nitrogen in air- 
drying. 



INTERNAL WORK. 



387 



in the manner described on page 76 on the assumption that the fat 
has the composition C 76.54 per cent., H 12.01 per cent., O 11.45 
per cent., and the carbohydrates that of starch. 

Fifth, on the basis of the chemical processes thus computed the 
amount of energy set free is estimated from the known (average) 
heats of combustion of the materials oxidized. 

While the calculation involves numerous assumptions, and 
while, therefore, the result is of the nature of an approximation 
most of the assumptions are so nearly correct as not to contain the 
possibility of serious error. The two which seem most questionable 
are the peculiar method of computing the digestibility of the food 
and the proteid metabolism, and the computation of the proximate 
composition of the urine. 

Influence of Food Consumption on Metabolism. — The 
influence of the ingestion of food in increasing the oxygen con- 
sumption and the energy metabolism of the animal is illustrated by 
the following tabulation of the results obtained in Period b (loc. cit., 
p. 282). (The animal was standing quietly, but otherwise was in 
a state of rest.) 





In the Morning, 
Fasting. 


Immediately After Feeding. 


Later Stage After 
First Feeding. 


No. of 
Experiment. 


Per Kg. Live 

Weight per 

Minute. 


03 

<D bi 

bio 

3 



n 


Feed Eaten. 


Per Kg. Live 

Weight per 

Minute. 


tn 

03 

« 

a 03 

? 



n 


Per Kg. Live 

Weight per 

Minute. 


43 

03 




gig 

og 



a S g 


Oats 

and 

Straw, 

Grms. 


Hay, 

Grms. 


C 05 

sis 

O 
O 


a 3 g 


81 

* 1 ° 

og 



O 05 O 


CO t 

■£§ 

S 
O 


49 








T2300 
|_2300 

2100 
2280 
3180 
3150 
[2300 
2330 

[0 


1500"! 
1500 J 

1000 
1420 


1000] 
1430 
1650 
2500] 








3.602 
3.613 

3.823 
3.737 
3.739 
3.169 
3.564 

4.174 
3.914 


18.365 
18.798 

19.159 
19 . 220 
19.304 
16.134 
18.318 

20.450 
19.333 


3 5 


50 














2 


51 


3.226 
3.304 
3.516 
3.246 
3.130 
3.499 
3.310 


16.380 
16.784 
17.613 
16 . 359 
16.928 
17.748 
16.219* 


10.5 
10.5 
10.5 
11.0 
10.5 
11.0 
17.5 


3.418 
4.039 
3.745 
3.584 


17.431 
20.889 
18.913 
17.647 


0.6 
0.8 
0.5 
0.6 




52 




53 




54 


4 5 


55 


4 5 


56 


3 5 


57 


4 


58 


2.5 


59 


3.475 
3.446 
3.242 


17.516 
17.474 
16.272 


11.0 
11.0 
11.0 


3.716 
3.385 


18.931 
17.247 


0.5 
0.5 




60 


3 5 


61 


3.5 












Averages . . 


3.339 


16.929 


11.5 


2173 


917 


3.648 


18.510 


0.6 


3.704 


18.787 


3.5 



* Animal was uneasy. 



3 88 



PRINCIPLES OF ANIMAL NUTRITION. 



The average energy metabolism thirty-six minutes after eating, 
computed as previously described, is somewhat more than 9 per cent, 
greater than that shortly before eating, and a still further increase 
was observed at the end of three hours. The effect is precisely 
similar to that observed in Magnus-Levy's experiments. It was 
not, however, followed through the twenty-four hours, as in some 
of those experiments. 

Comparison of Hay and Grain.— It was found further that 
coarse fodder (hay) produced a much more marked effect than did 
grain. The following comparison of the average of the experi- 
ments of Period c on an exclusive hay diet with that of Period / on 
a mixed ration illustrates this fact : 





Period c. 


Period /. 


Time since last fed 


2.6 hrs. 
About 10.5 kgs.* 


2.8 hrs. 

4.75 kgs. 
6.00 " 
1.00 " 

5697 . grms.f 

3.6986 c.c. 

3.6695 " 

18.339 cals 


Ration : 

Hay 


Oats 


Straw 




Total digested nutrients (fat X 
2.5) 


4125 grms. f 

3.9837 c.c. 

3.6586 " 

19.552 cals. 


Per kilogram and minute: 
Oxygen consumed 


Carbon dioxide given off . . . 
Energy set free (computed) 



Notwithstanding the greater total weight of food consumed in 
Period /, and the much larger amount of digestible matter contained 
in it, the oxygen consumption and the computed amount of energy 
liberated are notably greater in Period c, on the hay ration. The 
average time which had elapsed since the last feeding, as well as the 
external conditions, having been substantially the same in both 
periods,! and the animal having been in a state of rest, the effect 
is ascribed to an increase in the expenditure of energy in diges- 
tion due to the difference in the physical properties of the two 
rations. This difference is chemically characterized by the greater 

* The exact amount of hay eaten is not stated. The digestible matter 
is computed from the composition of the hay by the use of Wolff's coeffi- 
cients. 

t Computed in the manner described above, p. 386. 

$ It varied considerably in the individual experiments composing Period /. 



INTERNAL WORK. 389 

proportion of crude fiber in the hay ration. Ascribing the differ- 
ence in digestive work entirely to the crude fiber, the authors en- 
deavor to estimate the expenditure of energy on this ingredient 
as follows: 

Digestive Work for Crude Fiber. — The hay ration con- 
tained 1572 grams less of (estimated) digestible matter and 648 
grams more of total crude fiber than the mixed ration. The com- 
puted evolution of energy per head for the twenty-four hours was 
greater by 772 Cals. in the hay period. On the basis of Magnus- 
Levy's results the authors assume that the expenditure of energy 
in the digestion of the nutrients exclusive of crude fiber equals 9 
per cent, of the total energy of the digested matter. For 1572 
grams (fat being reduced to its starch equivalent) this amounts to 
4.1X1572X0.09 = 580 Cals. Accordingly, the energy metabo- 
lism should have been 580 Cals. less in Period c than in Period /. 
It was actually 772 Cals. greater, a difference of 1352 Cals. This 
difference is ascribed to the presence of the 648 grams more of total 
crude fiber, and corresponds to 2.086 Cals. per gram. With an 
average digestibility of 55 per cent, this would equal 3.793 Cals. 
per gram of digested crude fiber, an amount slightly exceeding its 
metabolizable energy as computed on p. 331. In other words, it 
would appear that all the metabolizable energy of the crude fiber 
(or even more, should the digestibility fall below the percentage 
assumed) is consumed in the work of digestion and converted into 
heat, leaving none available for external work, and this result seems 
to coincide strikingly with the results obtained by Wolff * by an 
entirely different method. (Compare Chapter XIII, §2.) 

It is to be observed, however, that the basis of Zuntz & Hage- 
mann's computation is the difference between the energy required 
for the digestion of the 648 grams of crude fiber and that required 
for the digestion of an equal amount of fiber-free nutrients. To 
get at the total expenditure upon the digestion of the crude fiber 
we should make the following computation: 

The nutrients other than crude fiber digested were in Period / 
5124 grams and in Period c 2608 grams, a difference of 2516 grams. 
The corresponding difference in the work of digestion would, on the 

* Grundlagen, etc., Neue BeitrSge, 1887, p. 94 



39° PRINCIPLES OF ANIMAL NUTRITION. 

above assumptions, be 4 . 1 X 2516 X . 09 = 928 Cals. Adding this, 
as before, to the observed difference of 772 Cals. gives a total of 
1700 Cals. as the effect of the 648 grams of crude fiber, which equals 
2.623 Cals. per gram. With a digestibility of 55 per cent., this 
corresponds to 4.768 Cals. per gram of digested crude fiber, or 
materially more than its metabolizable energy. 

Uncertainties of the Computation. — The whole method of 
computation, however, is open to serious criticism on at least two 
points, aside from the rather indefinite statements as to the amount 
of hay consumed in Period c and as to the distribution of the ration 
between the three feedings in Period /. 

First, the estimate for the work of digestion of the nutrients 
other than crude fiber which forms the basis of the computation is 
derived chiefly from the experiments of Magnus-Levy on dogs and 
man. Those experiments were not only made with highly digesti- 
ble food, but the digestive work is computed as a percentage of the 
total (gross) energy of the food. The food of the horse contained 
in the dry matter 40.94 per cent, of indigestible substances in 
Period / and 54.37 per cent, in Period c, or if we leave out of account 
the crude fiber the corresponding figures are 31.99 per cent, and 
58.45 per cent. A considerable part of the work of digestion un- 
doubtedly' consists of muscular work, which must be performed 
on the indigestible as well as the digestible matter of the food. 
Moreover these indigestible matters, by their mechanical stimulus 
and by acting in a certain sense as diluents, may perhaps cause a 
more abundant secretion of the digestive juices. These facts are 
entirely ignored when the figures for digestive work derived from 
experiments on dogs and man are applied simply to the digested 
food of the horse. 

Second, the method of computation assumes that the difference 
between the metabolism on the two rations which was observed 2.7 
hours after eating would have retained the same absolute (not rela- 
tive) value during the twenty-four hours. The justification for this 
assumption is found in a comparison * of the results of a single res- 
piration experiment, made one half hour after feeding, with the 
average of two experiments in which the excretion of carbon 

* Loc. cit., p. 218. 



INTERNAL WORK. 39 x 

dioxide was determined for twenty-four hours in a Pettenkofer 
respiration apparatus. After allowing for the work of mastica- 
tion in the latter experiment the results were found to agree 
within 8.8 per cent. The authors, therefore, conclude that with 
regular feeding the respiratory exchange during the forenoon 
hours, when their experiments were made, corresponds substan- 
tially to the average metabolism for the twenty-four hours, exclu- 
sive of the work of mastication. It is to be remarked, however, 
that this conclusion is not fully in harmony with the results 
quoted on p. 387, which plainly show a marked decrease in the 
metabolism during the night. Moreover, numerous other deter- 
minations of the respiratory exchange at the same hours and on 
similar food show quite wide variations. In view of this discrep- 
ancy, as well as of the somewhat narrow basis of comparison, it 
certainly appears questionable whether a computation of Periods 
c and / for twenty-four hours can be safely made. 

Zuntz & Hagemann's results unquestionably show that the 
work of digestion is greater with coarse fodder than with grain. 
That this difference is due, at least in large part, to the greater 
amount of crude fiber in the former is extremely probable. In 
view, however, of the two sources of uncertainty just pointed out, 
as well as of the numerous minor assumptions involved in the calcu- 
lations, we must conclude that the data available are insufficient 
for an accurate quantitative estimate of the digestive work re- 
quired by crude fiber. 

Work of Mastication. — The foregoing computations relate 
to the expenditure of energy in the digestion of the food after it has 
entered the stomach. The same authors have also determined the 
increase in the gaseous exchange caused by mastication, degluti- 
tion, etc. For this purpose they compare * the excretion of carbon 
dioxide and the consumption of oxygen during the time actually 
occupied in eating with the corresponding amounts during rest as 
found from the average of a number of experiments made under 
identical conditions. On the assumption that the proteid metabo- 
lism is unaltered, the proportion of carbohydrates and fat metabo- 
lized and the corresponding amounts of energy are computed by 

* Loc. cit., p. 271. 



39 2 



PRINCIPLES OF ANIMAL NUTRITION. 



the method described on pp. 76 and 252. The following is a sum- 
mary of the results computed per kilogram of feed : 



Fodder. 


No. of 
Experi- 
ments. 


Oxygen 

Consumed, 

Liters. 


CO a 

Excreted, 
Liters. 


Equivalent 

Energy, 

Cals. 


Oats and cut straw (6:1).... 
Hay 


8 
8 
8 
2 

7 


12.964 

33.840 

20.072 

7.133 

6.171 


10.679 

27.813 

17.677 

6.205 

4.980 


64.17 
167.44 


Hay, oats, and cut .... / 

Maize and cut straw (6:1)... 


100.79 
35.72 
30 42 


Computed for oats alone 


47.00 


" maize alone . . . 








13.80 













As was to have been expected, the work of mastication proves 
to be much greater in the case of hay than in that of grain. Maize 
gave a remarkably low result, while the lowest was obtained with 
green fodder. Even when the results on the latter are computed 
per kilogram of dry matter, they are still about 40 per cent, lower 
than those on hay. A few experiments on old horses with defect- 
ive teeth gave somewhat higher results for the mixture of oats 
and cut straw. 

The absolute amount of energy expended in mastication, etc., is 
very considerable. On the average of three periods, on a ration 
consisting of 5.6 kgs. of oats, 0.93 kgs. of cut straw, and 5.18 kgs. 
of hay, it is computed at 1287.1 Cals., an amount equal to 11.2 per 
cent, of the total metabolism during rest. 

Conclusions. — The researches of Zuntz & Hagemann are of 
great value in that they demonstrate the large proportion of the 
energy of the food which is consumed in its prehension, mastication, 
digestion, and assimilation in the case of herbivorous animals, and 
that this proportion is largely influenced by the physical character 
of the food. Thus the hard but brittle maize required much less 
energy for its mastication than the softer but tougher and more 
woody oats, and the dry matter of the green alfalfa decidedly less 
than that of the hay. These results indicate quite clearly that no 
accurate estimates of the work of mastication can (at least in the 
present state of our knowledge) be based on the chemical compo- 
sition of feeding-stuffs. As noted above, Zuntz & Hagemann 
attempt to compute the work of digestion upon that basis. It 



INTERNAL WORK. 393 

certainly seems open to question, however, whether in this case also 
other properties than those expressed by the percentage of crude 
fiber may not materially affect the result,* and it will be wise, until 
the subject receives further investigation, to accept their compu- 
tations as tentative and approximate.! 

* Compare Kellner's results on cattle, Chapter XIII, § 1. 

f A somewhat extended critique by Pfeiffer of these researches, together 
with replies by Zuntz & Hagemann, will be found in Landw. Vers. Stat., 54, 
101; 55, 117; 56, 283 and 289. 



CHAPTER XII. 
NET AVAILABLE ENERGY— MAINTENANCE. 

The organic matter contained in the body of an animal we have 
learned to regard in the light of a certain capital of stored-up energy, 
at the expense of which the vital activities of the organism are 
carried on. The function of the food is to make good the losses 
thus occasioned. The food is frequently spoken of as "the fuel of 
the body." In a certain limited sense the comparison is admissible, 
but it may easily be pushed too far, and a closer analogy is that with 
a stream of water supplying a reservoir and serving to replenish the 
drafts made upon it for water. 

The food in the form in which it is consumed, however, is by no 
means ready to enter directly into the composition of the tissues of 
the body and add to its store of potential energy, but on the con- 
trary, as we have seen, a very considerable amount of energy must 
be expended in the separation of the indigestible matters from the 
digestible and in the conversion of the latter into such forms as are 
suitable for the uses of the living cells of the body. 

When, therefore, we give food to a quiescent fasting animal we 
do two things : we supply it with metabolizable energy, depending 
in amount upon the quantity and nature of the food, to take the 
place of the energy expended in its internal work, but we at the 
same time increase its expenditure of energy by the amount neces- 
sary to separate the metabolizable from the non-metabolizable 
energy of the food. 

The case is analogous to that of a steam-boiler which is fired 
by means of a mechanical stoker driven by steam from the same 
boiler. Each pound of coal fed into the fire-box is capable of 
evolving a certain amount of heat, representing its metabolizable 
energy in the above sense, and that heat is capable of producing a 

394 



NET AVAILABLE ENERGY— MAINTENANCE. 395 

certain quantity of steam. A definite fraction of the latter, how- 
ever, is required to introduce the next pound of coal into the furnace 
and therefore is not available for driving the main engine. To 
recur to the illustration of the reservoir, it is as if the water, instead 
of simply flowing into the reservoir, actuated a pump or a hydraulic 
ram which lifted part of it to the required level. 

Gross and Net Availability. — As stated in Chapter X, the 
difference between the potential energy of the food and that of the 
excreta represents the maximum amount of energy which is avail- 
able to the organism for all purposes. This quantity has some- 
times been designated as gross available energy, but has here been 
called metabolizable energy. 

A portion of this metabolizable energy, however, as just pointed 
out, has to be expended in the various processes which have been 
grouped together under the term work of digestion and assimilation. 
This portion ultimately takes the form of heat, thus tending to 
increase the heat production of the animal by a corresponding 
amount, and becomes unavailable for other purposes in the body, 
since, so far as we know, the organism has no power to convert heat 
into other forms of energy. The remainder of the metabolizable 
energy of the food represents the amount which that food con- 
tributes directly towards the maintenance of the capital of potential 
energy in the body. It is the measure of the net advantage derived 
by the body from the introduction into it of the food.* From this 
point of view the energy remaining after deducting the expenditure 
caused by the ingestion of the food from its metabolizable or gross 
available energy has been called the net available energy. There 
are obvious objections to the use of the words available and avail- 
ability in two senses, but no better term for net available has 
yet been suggested, while the use of available energy in the sense 
of metabolizable energy has become quite general. It appears 
necessary, therefore, to retain for the present the modifying words 
gross and net to avoid ambiguity. 

Distinction between Availability and Utilization. — The 
net available energy of the food in the above sense represents the 

* As will appear later, this somewhat broad statement appears to be sub- 
ject to modification in certain cases in which there is an indirect utilization 
of the heat resulting from the work of digestion and assimilation. 



396 PRINCIPLES OF ANIMAL NUTRITION. 

net contribution which it makes to the demands of the vital func- 
tions for energy or, in other words, its value as part of a mainte- 
nance ration. This must be clearly distinguished from its value 
for the storage of additional energy in the body — that is, its value 
for productive purposes. In the latter case it is quite possible that 
the conversion of the digested nutrients into suitable forms for 
storage (fat of adipose tissue, ingredients of milk solids, proteids of 
new growth, etc.) involves a greater expenditure of energy than is 
required to convert them into forms fitted to serve as sources of 
energy to the body cells (work of assimilation). The consideration 
of this question belongs in the succeeding chapter, but meanwhile 
it is important to bear in mind that the net available energy, in 
the sense in which the term is here employed, is a distinct con- 
ception from that of the utilization of energy in fattening, milk 
production, etc., and has reference to the availability of the energy 
of the food for maintenance. 

It is evident from the above paragraphs that the value of a 
feeding-stuff to the animal is not measured solely by its metaboliz- 
able energy, since materials containing the same proportion of the 
latter may require the expenditure of very unequal amounts of 
energy for their digestion and assimilation and, therefore, may 
contain very unequal amounts of net available energy. Plainly, 
then, it is a matter of much importance to know the net avail- 
ability of the metabolizable energy of the various nutrients and 
feeding-stuffs, and thus to learn the proportions in which they may 
replace each other. 

§ 1. Replacement Values. 

We have already seen (Chapter V, p. 148) that, aside from a 
certain minimum of proteids, the several nutrients can mutually 
replace each other to a very large if not to an unlimited extent, 
either one or all serving, according to circumstances, to supply the 
demand for energy. 

In 1882 v. Hosslin * published an extended discussion of Petten- 
kofer & Voit's respiration experiments from this point of view, 
using such data regarding the potential energy of the nutrients as 
were then available. He calls attention to the wide range of re- 

* Virchow's Archiv, 89, 333. 



NET AVAILABLE ENERGY— MAINTENANCE. 



397 



placement possible, quoting also Lawes & Gilbert's conclusions * 
on the same point drawn from their experiments on fattening swine, 
and asserts that the nutrients replace each other according to their 
content of available energy. Danilewsky f also advanced similar 
views, but Rubner % appears to have been the first to investigate 
the subject experimentally. 

Isodynamic Values. — We have already seen that the total 
metabolism of a fasting animal is approximately constant, repre- 
senting the rate at which the store of matter and energy in the body 
is drawn upon to support the necessary internal work. If we deter- 
mine the total metabolism of such an animal and then give it a 
known quantity of some nutrient, as fat, e.g., the loss of tissue will 
be diminished by a certain amount, which will represent the net 
available energy of the nutrient and which may be compared with 
the amount fed. Similarly, a second and third nutrient may be fed 
and thus their relative values for the prevention of loss of tissue be 
determined. For example, a dog after fasting for six days was 
given on the seventh and eighth days 720 and 760 grams respect- 
ively of fresh lean meat. The average nitrogen and fat metab- 
olism for the fifth and sixth days (fasting) and the seventh and 
eighth days was as follows : § 



Food. 


Total Nitrogen 

Excretion 

Grms. 


Fat 

Metabolized 

Grms. 


Temperature 
Deg C. 


Nothing (fifth and sixth days) .... 
Meat (seventh and eighth days) . . 


3.16 
20.63 


75.92 
30.72 


18.0 
19.2 


Difference . . . .' 


+ 17.47 


-45.20 


+ 1.2 







The result of the feeding with meat was, of course, a great in- 
crease in the proteid metabolism. The increase of 17.47 grams in 
the nitrogen excreted was equivalent to 113.38 grams of dry matter 
of the meat. The metabolism of this amount of proteid matter, 
therefore, enabled the organism to diminish the metabolism of fat 

* Phil Trans , 160. 541 

f Die Kraftvorrate der Nahrungsstoffe ; Arch. ges. Physiol., 1885. p. 230. 
% Zeit. f. Biol , 19, 313 

§The original account of the experiments is contained in Zeit. f. Biol., 
19, 313; these figures are the corrected values given in ibid., 22, 45. 



39« 



PRINCIPLES OF ANIMAL NUTRITION. 



by 45.20 grams. For the prevention of loss of tissue in this experi- 
ment, then, 250 parts of the dry matter of the meat were apparently 
equivalent to 100 parts of fat. The food, however, was given at the 
temperature of the room. To warm it and the 100 c.c. of water 
consumed to the temperature of the body would require an amount 
of heat equal to that produced by the oxidation of 1.4 grams of fat. 
Adding this to the 45.2 grams above gives 46.6 grams of fat as the 
equivalent of 113.3S grams of dry matter of the meat, or a ratio of 
100:243. 

Another similar experiment gave as a final result a ratio of 
100: 253, or after correction for the warming of the food 100: 243, 
and a third longer experiment with extracted lean meat (syntonin) 
yielded the ratio 100: 227, or corrected as before 100: 225. 

If now, from the results of Rubner's determinations of the met- 
abolizable energy of the proteids (p. 276), we compute the amount of 
each which contains the same quantity of metabolizable energy as 
100 grams of fat and compare it with the above ratios we have the 
following as the amounts equivalent to 100 grams of fat : 



Dry Matter of — 


Computed 
from Met- 
abolizable 
Energy, 
Grms. 


Found in 

Experiments 

on Animals, 

Grms. 


Lean meat: 

First experiment 

Second " 

Extracted meat 


235 
235 
213 


243 
243 
225 





The computed and observed equivalents differ by only 4.3 per 
cent, and 5.6 per cent, respectively, and hence Rubner concludes 
that protein replaces fat in metabolism substantially in inverse pro- 
portion to its " physiological heat value," or, in other words, to its 
metabolizable energy. 

Rubner has also made similar experiments with cane-sugar and 
starch, comparing them in each case with the body fat, as in the 
above experiments, and has also made trials in which grape-sugar 
was substituted for the fat of the food. In computing the results 
of these experiments any change in the proteid metabolism was 
reduced to its equivalent in fat as computed from its metabolizable 



NET AVAILABLE ENERGY-MAINTENANCE. 



399 



energy. The following table contains the final results, including 
those on proteids just given: 



EQUIVALENT TO 100 GRMS. OF FAT. 



Dry Matter of — 


Computed 

from 

Metabolizable 

Energy, 

Grms. 


Found in 

Experiments 

on Animals, 

Grms. 


Lean meat 


235 
213 

235 

229 

255 


243 

243 

225 

( 234 

\ 235 

( 234 

232 

( 258 

■J 254 

( 255 


Extracted meat 


Cane-sugar 


Starch 


Grape-sugar 





The equivalents found by experiment correspond quite closely 
with those computed from the metabolizable energy, and on these 
facts Rubner bases the law of isodynamic replacement, which may 
be briefly stated as follows: In amounts less than a maintenance 
ration the nutrients replace each other in inverse proportion to their 
metabolizable energy. The quantities which thus replace each other 
are accordingly said to be isodynamic. It need scarcely be pointed 
out that the minimum of proteids required for the maintenance of 
the nitrogenous tissues is not included under this law. 

Rubner is careful to limit this law to small amounts of food. 
In his earlier publications he states that it holds only below the main- 
tenance ration ; later * he asserts that it obtains up to an excess of 
about 50 per cent, over the maintenance ration. 

Isoglycosic Values. — Mention has already been made of the 
theory of isoglycosic values maintained by Chauveau and his school, 
according to which the net available energy of the digested nutrients 
is measured by the amount of sugar they are considered to be capa- 
ble of producing in the organism according to the equations given 
in Chapter II. Chauveau | computes that the metabolism of 100 
parts of proteids according to Gautier's scheme (p. 51), together 
with the partial oxidation of the resulting fat (p. 38), would yield 
* Biologische Gesetze, p. 20. f Comptes rend., 126, 1073. 



400 



PRINCIPLES OF ANIMAL NUTRITION. 



81.5 parts of dextrose. Laulanie* * computes that 100 parts of 
fat, carbohydrates, and albumin would produce the following 
amounts of dextrose : , 

100 parts of fat produce 161 parts of dextrose 

100 " " starch produce 110 " " " 

100 " " sucrose produce 105 " " " 

100 " " albumin produce 80 " " " 

The corresponding isoglycosic values would be as follows, 
Rubner's isodynamic values being added for comparison: 





Isodynamic 
Weights. 


- - ~ 

Isoglycosic 
Weights. 


Fat 


100 
229 
235 
255 
235 
213 


100 
146 
153 
161 

201 


Starch 


Cane-sugar 


Dextrose 


Extracted meat 


Albumin 





It is evident that the chief point of difference is the relative 
value of fat and carbohydrates. 

Experiments on Maintenance. — As regards the relative values of 
the several nutrients in a maintenance ration the above conclusions 
are in part based on theoretical considerations and in part are de- 
ductions from the experiments upon the influence of work on the 
respiratory quotient and upon the nature of the non-nitrogenous 
material metabolized which were considered in Chapter VI, pp. 
211 to 225. Contejean,f however, has made direct experiments 
upon the replacement values of fat and carbohydrates. 

His experiments were made with dogs. In the first series the 
animal, weighing about 20 kgs., received a basal ration of 500 grams 
of meat (1000 in the first period), estimated to be ample to main- 
tain nitrogen equilibrium. To this were added in the several 
periods varying amounts of lard, sugar, and gelatin. The live 
weight of the animal was taken daily at the same hour and under 
uniform conditions, and the urinary nitrogen was determined. 
No mention is made of the fecal nitrogen. The total heat produc- 

* Energetique musculaire, p. 101. 
| Archives de Physiol., 1896, p. 803. 



NET AVAILABLE ENERGY— MAINTENANCE. 



401 



tion for the four days of each experiment (excluding preliminary 
feeding) is computed from the proteid metabolism as measured 
by the urinary nitrogen, on the assumption that all the fat con- 
tained in the meat and all the non-nitrogenous nutrients added 
were metabolized. An exception is made in the fourth period, 
however, in which the author computes from a comparison of the 
gains of nitrogen and of live weight that there was a gain of about 
50 grams (?) of fat by the animal. The results are contained in 
the first six columns of the following table : 









Gain or 

Loss of 

Weight, 

Grms. 


Gain or Loss of 


Esti- 
mated 
Heat 
Pro- 
duction, 
Cals. 


Cor- 
rected 


T3 



PM 


Food. 


Nitrogen, 

Grms. 


Equivalent 
Flesh, 
Grms. 


Heat 
Pro- 
duction, 
Cals. 


I 


1000 grms. meat 


-395 
-170 

+ 50 

+ 335 (?) 

+ 152 

-105 


+ 19.39 

- 1.86 

+ 1.81 
+ 6.36 
+ 6.04 

- 1.10 


+ 570 

- 55 

+ 53 
+ 187 (?) 
+ 170 

- 32 


4548 
3903 

5326 

5486 

3811 

4088 


6190 




500 " " 






II | 
III] 

ivj 

vj 

VI 1 


40 " lard 
500 " meat. . . 

80 " lard 
500 " meat . . . 
100 " lard 
500 " meat. . . 
100 " sugar . . 
500 " meat.. . 
100 " gelatin . 




4981 
5354 
4566 
3980 
4773 



Making the comparison of fat and carbohydrates, as the essen- 
tial point, it would appear from Contejean's results that 100 grams 
of sugar was fully as efficient as 80 grams of fat, while according 
to Rubner's figures about 180 grams of sugar would be required. 
Corresponding to this is the lower computed heat production in the 
sugar period, the excess in the fat periods being ascribed to the 
cleavage of fat believed to occur in the liver. 

If, however, there is justification for computing the gain of fat 
by the body in the fourth period by subtracting the gain of flesh 
from the total gain in weight, the same method is equally applicable 
to the other periods. By its use the figures of the last column of 
the table have been computed by the writer. While the heat 
production in the sugar period as thus estimated is still below that 
of the fat periods, the rather wide range in the results of the latter 
serves to illustrate the uncertainties of such computation. 



4-0 2 



PRINCIPLES OF ANIMAL NUTRITION. 



In a second series of experiments a ration of 150 grams of meat 
and 100 grams of lard appeared to be equivalent to one of 300 grams 
of meat and 50 of lard. In a third series, fat, sugar, and gelatin 
were each given for two days to a fasting dog, the live weight * and 
urinary nitrogen being determined daily. The results were as 
follows : 



Date. 


Live Weight, Kgs. 


Food. 


Urinary 

Nitrogen, 

Grms. 


Dec. 24 


25 . 780 

25 . 125 

24.765 

24. 780 +.095 feces 

24. 616 +.064 " 

24.215 

23.920 

23. 870 +.038 " 

23.500 

23.200 


Nothing 

it 

a 

200 grms. sugar 

200 " 

Nothing 

200 grms. fat 

200 " 

Nothing 

200 grms. gelatin 




" 25 


5.56 


" 26 


6.05 


" 27 


5.59 


" 28 


4.13 


" 29 


4.59 


" 30 


6.56 


" 31 


6.85 




4.97 


" 2 


28.77 







Neglecting the variations in the urinary nitrogen, Contejean 
makes the following comparison of the daily loss of live weight, 
from which he draws the conclusion that 200 grams of sugar, 
equivalent to 792 Cals., was more efficient in maintaining the ani- 
mal than 200 grams of fat, equivalent to 1876 Cals. 

Gain or Loss of Live Weight per Day. 

Average for fasting —377 grams 

Sugar : 

First day +110 grams 

Second day -100 " 

Average +5 

Fat: 

First day -295 grams 

Second day — 12 

Average — 154 

* In taking the live weight any feces voided during the previous twenty- 
four hours were added to the weight of the animal, so that the computed gaiu 
or loss of weight does not include the feces. 



NET AVAILABLE ENERGY— MAINTENANCE. 403 

Experiments in which Work was Done. — Somewhat earlier in 
point of time than the above experiments by Contejean were similar 
ones by Chauveau * in which the animal performed a uniform 
(unmeasured) amount of work per day. No attempt was made to 
determine the equivalence between food or body metabolism and 
the work performed, but the latter was simply used as a means of 
increasing the metabolism, while the relative value of the several 
nutrients in maintaining the store of energy in the body was esti- 
mated from the effect upon the live weight. The experiments, 
therefore, are not, properly speaking, work experiments, but belong 
in the same category as those of Contejean — that is, they aim to 
show in what proportions the nutrients may replace each other in 
a maintenance ration. 

In the first series the basal ration consisted of 400 grams of 
lean meat, to which was added in alternate six- or five-day periods 
either 51 grams of lard or an isodynamic quantity (121 grams) of 
cane-sugar. In one period 128.5 grams of dextrose was used in- 
stead of the cane-sugar. The animal (bitch) averaged about 16.8 
kgs. in weight. The gain or loss of weight in each period (differ- 
ence between first and last weighings) was as follows : 

' Period 1. . . .- Lard grams 

" 2 Cane-sugar + 170 " 

" 3 Lard - 10 " 

" 4 Cane-sugar +290 " 

" 5 Lard -265 " 

" 6 Dextrose " 

" 7 Lard -295 " 

In the first four periods the cane-sugar seems to have caused a 
gain in weight as compared with practical maintenance on the lard. 
During the last three periods the animal was in heat and a loss of 
weight upon the lard ration resulted, which was arrested on the 
dextrose ration. Water was given ad libitum for several hours after 
the work, but withdrawn at least twelve hours before weighing. 
No record is given of the amount of it consumed or of the water 
content of the materials fed. 

In another experiment, in which twice as much work was done, 

* Comptes rend., 125, 1070; 126, 795, 930, 1072. 



4°4 PRINCIPLES OF ANIMAL NUTRITION. 

fat and cane-sugar replaced each other in isoglycosic proportions, 
viz., 110 grams of fat and 168 of cane-sugar. In this case the 
amount of water consumed was uniform, viz., 400 grams. The gain 
or loss of live weight in five-day periods was : 

Period 1 Sugar -f- 35 grams 

" 2 Fat -160 " 

" 2 " —Omitting first day . . - 20 " 

A third experiment, in which amounts of sugar intermediate 
between the isoglycosic and isodynamic equivalents of the fat 
were fed, showed a gain on the former as compared with practi- 
cally no change on the fat. 

In a second series of experiments isoglycosic amounts of lard 
(110 grams) and cane-sugar (168 grams) were alternated every five 
or three days for eighty-five days, the basal ration consisting of 500 
grams of lean meat, and 400 grams of water being consumed per 
day. The estimated heat values of these rations were respectively 
1513 Cals. and 1145 Cals., but notwithstanding this difference they 
appeared to be equally efficient in maintaining the live weight. 

Whatever weight may attach to the deductions from the exper- 
iments upon work production, it is hardly necessary to urge that 
such a method of investigation as that employed in the above 
trials, while it may afford useful indications, is altogether too 
crude to disprove the theory of isodynamic values based upon 
Rubner's more elaborate experiments. 

Respiration Experiments. — Kaufmann * has also reported respi- 
ration experiments in support of the views regarding the interme- 
diary metabolism promulgated by Chauveau. In his experiments 
the nitrogen excretion, respiratory exchange, and heat production 
of dogs variously fed were determined, in five-hour periods, by 
means of a radiation calorimeter in which the products of respira- 
tion were allowed to accumulate. (See pp. 69 and 248.) From the 
theoretical equations given in Chapter II he computes the figures 
given on the opposite page for the consumption of oxygen, produc- 
tion of carbon dioxide, and heat evolution in the various reactions. 

Besides determinations of the fasting metabolism the experi- 
ments included feeding exclusively with meat and also with rations 
rich in carbohydrates and in fat. For each diet, on the basis of the 
* Archives de Physiol., 1896, pp. 329, 342, and 757. 



NET AVAILABLE ENERGY— MAINTENANCE. 



405 





Per Grm. of Substance. 


Heat 




Oxygen 

Con- 
sumed, 
Liters. 


Carbon 

Dioxide 

Produced, 

Liters. 


Heat 

Evolved, 
Cals. 


of Oxygen 
Con- 
sumed, 
Cals. 


Albumin to fat and urea 


0.481 
0.713 
1.045 
0.840 
2.043 
0.744 


0.4777 
0.5480 
0.8720 
. 2257 
1.4290 
0.7440 


2.234 
3.180 
4.857 
3.417 
9.500 
3.762 


4.646 
4.460 
4.647 
4.067 
4.650 
5.056 


" C0 2 , H 2 " " 

Stearin " " " " dextrose . . . 

" " andH 2 

Dextrose " " " " 





determination of the respiratory products, the author assumes a 
scheme of metabolism in accordance with the theory, and finds that 
the heat production as computed on this assumption agrees quite 
closely with that actually determined. 

Aside from questions of method, particularly whether a five- 
hour period is sufficiently long, it is to be remarked that the results 
of Kaufmann's experiments are ambiguous. They show that it is 
possible to interpret the facts in accordance with his theory, but 
they do not exclude the possibility of other explanations. For this 
reason it seems unnecessary to cite the experiments in detail, and 
for the same reason they are at best but confirmatory evidence in 
favor of the theory of isoglycosic values. 



§ 2. Modified Conception of Replacement Values. 

The theory of isodynamic replacement as announced by Rubner 
constituted the first systematic application of the general laws of 
energy to the problems of animal nutrition. As such it has exerted 
a profound influence upon subsequent study of the subject in that 
it has been chiefly instrumental in leading to a practical application 
of the long-known fact that the food is primarily a supply of energy. 
It was based, of course, upon the conception that the law of the 
conservation of energy obtains in the animal body, and in subsequent 
experiments, which have been described in Chapter IX, Rubner 
gave at least a partial demonstration of the truth of this concep- 
tion. 

Rubner' s general ideas still form the basis of our views regard- 



406 PRINCIPLES OF ANIMAL NUTRITION. 

ing the metabolism of energy in the body, but, as was natural, his 
first conclusions have undergone more or less modification, in part 
at his own hands. 

Digestive Work. — The law of isodynamic replacement as 
stated above is equivalent to saying either that all the metabolizable 
energy of the food below a maintenance ration is net available 
energy or that the percentage availability of all the nutrients 
experimented with is the same. The latter supposition, however, 
appears to be negatived by the results of Magnus-Levy and others 
on digestive work. 

If, however, a fraction of the metabolizable energy of the food 
is applied to the work of digestion and assimilation, it is plain that 
this fraction cannot serve directly for tissue building. In his first 
paper, Rubner, while not denying the fact of the consumption of 
energy in digestive work, appears to regard its amount as insignifi- 
cant, although what he specifically claims is that the total metabo- 
lism below the maintenance ration is not increased by the inges- 
tion of food. In support of this view he gives the results of three 
experiments in which fat was fed; that is, the nutrient which, ac- 
cording to Magnus-Levy's later results, causes the least digestive 
work. Of these, one on a dog, in which approximately a mainte- 
nance ration was given, showed no increase of the metabolism over 
the fasting state. In the other two experiments, one on a dog and 
one on a rabbit, more fat was consumed than corresponded to the 
fasting metabolism, and an increase of the latter was observed 
amounting to approximately 3 per cent, and 12 per cent, respec- 
tively. Feeding with bone also caused an increase of about 12 
per cent. 

In a later publication,* however, he recognizes the apparent 
inconsistency between the effects of small and large amounts of 
food, and propounds a hypothesis to explain it which, in its general 
features at least, seems in harmony with the observed facts. This 
hypothesis is outlined in the following paragraphs, although in a 
slightly different manner than by Rubner. 

Indirect Utilization of Heat Resulting from Digestive 
Work. — In Chapter XI we acquired the conception of the critical 
thermal environment. According to the ideas there advanced, 
* Biologische Gesetze, Marburg, 1887, p. 20. 



NET AVAILABLE ENERGY— MAINTENANCE. 407 

the heat production of a quiescent, fasting animal below the critical 
point is made up of — 

1. The heat produced by the internal work. 

2. The heat produced by the processes of "chemical" regula- 
tion. 

The first of these we may regard as substantially constant, while 
the latter varies to meet varying conditions and thus maintain the 
constancy of body temperature. When we give food to such an 
animal we introduce a third source of heat, viz., the work of diges- 
tion and assimilation. Other conditions remaining the same, the 
tendency would be to raise the temperature of the body, and this 
tendency can be overcome either by means of " chemical " or " physi- 
cal" regulation. Recurring to the illlustration of the room on 
p. 356, it is as if a second fire were kindled in it. To maintain con- 
stant temperature, either the first fire must be lowered or the win- 
dows must be opened. 

The fact, however, that below the critical point the heat regula- 
tion of the body appears to be largely " chemical " renders it prob- 
able that the regulation is effected by the former method; that is, 
that the heat produced by the work of digestion is utilized to warm 
the body and that correspondingly less energy is withdrawn from 
that stored in the tissues of the body.* Under these circum- 
stances the total heat production of the animal would not be in- 
creased by the ingestion of food, and all the metabolizable energy 
of the food would be apparently available ; that is, we should have 
the phenomenon of isodynamic replacement. 

Digestive Work Above Critical Point. — The statements of 
the last paragraph refer to conditions below the critical point. 
Above this point no such indirect utilization of the heat resulting 
from digestive work is possible, since the heat production has 
already been reduced to the minimum due, as was concluded on 
p. 356, to internal work. The excess of heat arising from the work 
of digestion is then disposed of by " physical " means. 

Thus Rubner f obtained the following results for the carbon 

* Loewy (Arch. ges. Physiol., 46, 189; quoted by Magnus-Levy, ibid., p. 
116) claims to have shown that such a substitution or compensation does 
not take place in man. 

t Biologische Gesetze, pp. 17-25. 



408 PRINCIPLES OF ANIMAL NUTRITION. 

dioxide produced per square meter by guinea-pigs at 0° C. and at 
30° C. (critical temperature), when fasting and after the consump- 
tion of food ad libitum. 

PER SQUARE METER OF SURFACE. 



Fasting.* 






Fed. 




Live Weight, 
Grms. 


At 0° C. 
C0 2 , Grms. 


At 30° C. 
COj.Grms. 


Live Weight, 
Grms. 


At 0° C. 
CO,, Grms. 


At 30° C. 
CO.,, Grms. 


617 
568 
223 
206 


27.85 
30.30 
30.47 
31.56 


12.35 
10.53 
12.14 
13.16 


670 
520 
240 
220 

Average . . . 


29.49 
29.08 
34.07 
30.59 


14.10 
16.19 
17.69 
18.94 


Average. . . 


30.05 


12.05 


30.81 


16.73 



* Already cited on p. 366. 

Comparing the averages we see that at 0° C, considerably below 
the critical point, the consumption of food did not materially in- 
crease the total metabolism per unit of surface. On the other hand, 
at a temperature close to the critical point the average heat pro- 
duction was increased nearly 39 per cent, by the consumption of 
food. 

It appears also that at this higher temperature the heat produc- 
tion of the fed animals was no longer proportional to their surface, 
but was relatively greater in the smaller animals. Rubner explains 
this by the supposition that (the animals being fed ad libitum) the 
consumption of food by the animals was in proportion to their fast- 
ing metabolism ; that is, to their surface. Under these circumstances 
the factor of surface enters twice, and the heat production is approx- 
imately proportional to the square of the surface. 

Rubner * has also made calorimetric determinations of the heat 
production of a dog at different temperatures with the results 
shown on the opposite page. Not only did the feeding increase 
the heat production, but it eliminated the effect of rising tempera- 
ture in diminishing it; that is, it lowered the critical temperature. 

Critical Amount of Food. — The very probable hypothesis of 
a substitution of the heat produced by the work of digestion for that 

* Sitzungsber. der k. bayer. Akad. d. Wiss., Math.-phys. Classe, 15, 452. 



NET AVAILABLE ENERGY— MAINTENANCE. 



409 



Fasting. 


Fed Small Amount of Meat. 


Temperature, 
Deg. C. 


Heat 

Production, 

Cals. 


Temperature, 
Deg. C. 


Heat 

Production, 

Cals. 


13.2 
19.5 
27.4 


39.65 
35.10 

30.82 


19.5 

18.2 
23.7 
24.8 


42.64 
41.13 
41.83 
41.10 



arising, below the critical point, from the " chemical " regulation of 
the body temperature affords a very reasonable explanation of the 
apparent discrepancy between the law of isodynamic replacement 
as propounded by Rubner and the no less certain fact that the work 
of digestion and assimilation makes a demand on the body for 
energy, which energy finally takes the form of heat and is not 
available for other purposes. 

A consequence of this hypothesis, however, which is sufficiently 
obvious has indeed been pointed out, but hardly seems to have re- 
ceived the attention which it deserves in view of its important 
bearing on the theoretical aspects of metabolism. 

If we give increasing amounts of food to a fasting animal we 
progressively increase the evolution of heat due to digestive work, 
and this heat, according to the hypothesis, if the thermal environ- 
ment is below the critical point, is substituted for the heat pre- 
viously produced by the metabolism of tissue. There must be a 
limit to the possibility of this substitution, however, just as there 
must be to the " chemical " regulation of body temperature (p. 353), 
since otherwise there would be a ration on which all the heat of the 
body was derived from the work of digestion and the internal work 
was performed without evolution of heat. The limit is indeed the 
same in both cases and is reached when all the heat previously 
evolved by the processes of "chemical" regulation has been re- 
placed by the heat arising from digestive work. Beyond that 
point the conditions are the same as in the fasting animal above 
the critical point, and the excess of heat is gotten rid of by 
"physical" regulation. We may call the amount of food whose in- 
gestion produces the quantity of heat necessary to just reach this 
limit the critical amount of food. Below that amount the apparent 



4io 



PRINCIPLES OF ANIMAL NUTRITION. 



availability of the metabolizable energy of the food will be 100 per 
cent, or we shall have isodynamic replacement. Above that 
amount we shall have an availability depending upon the relation 
of the work of digestion and assimilation to the total metabolizable 
energy. 

Graphic Representation. — The critical amount of food will 
depend chiefly upon two things, viz., the distance below the critical 
thermal environment at which the experiment is made and the 
amount of energy that has to be expended in the digestion and 
assimilation of the food. The greater the former quantity, the 
more of the total metabolism of the animal will be due to the " chemi- 
cal " regulation and therefore capable of being replaced, while the 
greater the work of digestion the less food must be consumed to 
furnish by its digestive work the heat necessary to a complete 
substitution. 




On the two coordinate axes OX and OY let distances along OX 
represent the metabolizable energy of the food consumed and dis- 
tances along OY the effect of this food upon the store of potential 
energy in the body. In the first instance, let us take the case of a 



NET AVAILABLE ENERGY— MAINTENANCE. 4* I 

fasting animal and suppose the thermal environment to be at the 
critical point. The distance OA may then represent the loss of 
potential energy (tissue) from the body caused by the internal work. 
If now we supply the animal with food 80 per cent, of whose met- 
abolizable energy is available, with any given amount of energy 
thus supplied, as OB = AC, 80 per cent, of that energy, represented 
by CD, will serve to maintain the store of potential energy in the 
body, while 20 per cent., or DB' ', will be absorbed by the work of 
digestion, etc., and converted into heat. Accordingly if we assume 
that the work of digestion is proportional to the amount of food 
eaten, the line AD will indicate the availability of the particular 
food and may be represented algebraically by the equation 

y=ax, 

in which a = tan D AC ' = the percentage availability. 

We may also represent the heat production on the same axes. 
With no food it will be OE equal to OA. With an amount of food 
equal to OB it will be equal to OE + DB'^BF, and the line EF, 
expressed algebraically by 

y=(l-a)x, 

will represent the law of heat production. 

Let us next suppose that, the animal being again deprived of food, 
the external demand for heat is increased, by a fall of temperature, 
e.g., and that to meet this demand the metabolism is increased by 
an amount AG, and the heat production consequently by the equal 
amount EH. If we now give the same food as before, its real availa- 
bility will be unchanged and will be represented by the line GI, 
parallel to AD. Up to the critical amount of food, however, the 
heat resulting from the digestive work will, as we believe, be sub- 
stituted progressively for that represented by EH and resulting 
from the metabolism AG. The apparent availability, therefore, 
will be represented by the line GK, making an angle of 45° with the 
axes, and the heat production by the line HL, parallel to OX. 
When the food consumed reaches an amount OM at which the line 
GK intersects AD, the limit of this substitution is reached, since 
the amount of digestive work, KN, equals the amount of additional 
metabolism AG caused by the fall in temperature. In other words. 



412 PRINCIPLES OF ANIMAL NUTRITION. 

OM is the critical amount of food. Beyond this amount the energy 
expended in the work of digestion will become waste energy, serving 
simply to increase the outflow of heat, and the apparent and real 
availability of the food will coincide. 

Plainly, the critical amount of food will vary with circumstances. 
If the experiment is made at or above the critical thermal environ- 
ment for the fasting animal the smallest quantity must cause an 
increase in the heat production and the critical amount will be 
(or, mathematically, a negative quantity). As the external con- 
ditions fall below the critical thermal environment, the point K will 
be further and further removed from A until finally the point of 
intersection might even lie above OX, that is, above the mainte- 
nance ration. The relative availability of the food, too, will be a 
factor in determining the critical amount. Thus if the true availa- 
bility of the food were expressed by the line AP instead of AD, the 
point of intersection would lie at R and OR' would be the critical 
amount of food. 

§ 3. Net Availability. 

The modified conception of replacement values discussed in 
the preceding section and in the introductory paragraphs of this 
chapter renders it evident that both the theory of isodynamic re- 
placement, as first announced and later modified by Rubner, and 
the rival theory of isoglycosic replacement are but aspects of the 
more general question of the availability of the metabolizable 
energy of the food. That the* several nutrients are of use to the 
body and can replace each other in the food in inverse ratio to 
their available energy is simply a necessary consequence of the law 
of the conservation of energy. The important question is how 
much of their energy is really available. Rubner's theory regards 
all the metabolizable energy of the food as virtually available, 
directly or indirectly, for maintenance, and this view has been quite 
generally accepted. Chauveau's theory of isoglycosic replacement 
has the merit of distinctly recognizing the fact of a possible expen- 
diture of energy in the assimilation of the digested food, but, on the 
other hand, it takes no account of the digestive work, and moreover, 
so far as maintenance values are concerned, rests, as we have seen, 
upon a rather insecure foundation. Plainly, the real question at 



NET AVAILABLE ENERGY-MAINTENANCE. 413 

issue can only be settled by experiments in which the actual availa- 
bility of the energy of the food or of its various ingredients is deter- 
mined. 

Determinations of Net Availability. 

Since the net available energy of the food is equal to its metabo- 
lizable energy minus the energy expended in digestion and assimila- 
tion, the two general methods for the determination of the latter 
quantity which were outlined in the preceding chapter (p. 377) are 
also, from the converse point of view, methods for the determination 
of net availability. In our study of digestive work we considered 
chiefly the results of direct determinations of the increase in the 
heat production due to the ingestion of food; for our present pur- 
pose the results of any accurate determinations of the metabolism 
upon varying known amounts of the same food may be used. 

The experimental evidence available is far from being as full as 
could be wished, but in the following paragraphs the attempt has 
been made to summarize such data as are accessible. In consider- 
ing these results it should be remembered that, as explained on 
p. 396, the net available energy means the energy available for 
maintenance. In a considerable number of the experiments to be 
considered, more or less gain was made by the animals, but it seems 
better to give the results of each series of experiments in full, re- 
serving a discussion of the results with productive ration's for a 
subsequent chapter. 

Experiments on Carnivora. — The most extensive data regarding 
the metabolism of the carnivora in its relations to the food supply 
are those afforded by the investigations of Pettenkofer & Voit and 
of Rubner. These have already been considered in Chapter V 
from the standpoint of matter and chiefly in a qualitative way; 
we have now to study them quantitatively in their bearing upon 
the income and expenditure of energy by the body. 

In Pettenkofer & Voit's experiments, and in the earlier ones by 
Rubner, the quantities of energy involved must be computed from 
the chemical data. In Rubner's experiments upon the source of 
animal heat, cited in Chapter IX, the actual heat production of the 
animals was determined, but in no case was there a direct determi- 
nation of the total income and expenditure of energy, and in par- 
ticular the data as to the energy of the food are incomplete. For 



414 



PRINCIPLES OF ANIMAL NUTRITION. 



the study of replacement values by Rubner's method the latter 
factor was not necessary, but for a determination of the percentage 
availability of the energy of the food it is indispensable. In the 
following paragraphs the necessary computations of energy have 
been made by the writer, using Rubner's factors so far as possible.* 

In the case of Pettenkofer & Voit's experiments the average 
results given in Chapter V have been made the basis of the compu- 
tation. 

Proteids. — From the average results obtained by Pettenkofer 
& Voit f with different amounts of lean meat (see p. 104), the met- 
abolizable energy of the food and of the resulting gain (or loss) by 
the body may be computed as follows : 





Metabolizable 

Energy of 

Food, 

Cals. 


Computed Heat Production. 


Gain by 


Food, 
Grms. 


From 

Proteids, 

Cals. 


From Fat, 
Cals. 


Total, 
Cals. 


Body, 
Cals. 




500 

1000 

1500 




442 

883 

1325 


146 

530 

954 

1325 


895 
443 
179 

-38 


1041 

973 

1133 

1287 


-1041 
-531 
-250 

+ 38 



* The following factors were used in computing these experiments: 
Metabolizable Energy of Food : 

Bacon (Speck), 92.2 per cent, fat (Zeit. f. Biol., 30, 138). 

1 grm. pork fat, 9.423 Cals. {ibid., 21, 333). 

1 grm. butter fat, 9.216 Cals. (U. S. Dept. Agr., Office of Expt. Stations, 
Bull. 21, p. 127). 

1 grm. cane-sugar, 4.001 Cals. (Zeit. f. Biol., 21, 266). 

1 grm. grape-sugar, 3.692 Cals. (Stohmann, Zeit. f. Biol., 22, 40). 

1 grm. starch, 4.123 Cals. (Stohmann, ibid., 19, 376). 

Fresh lean meat, 3 . 4 per cent, nitrogen. 

1 grm. nitrogen in meat, 25.98 Cals. (Zeit. f. Biol., 21, 321). 

1 grm. nitrogen in syntonin, 26.66 Cals. (ibid., 21, 309). 
Energy of Metabolism : 

1 grm. excretory nitrogen (urine and feces). 

(a) No proteids fed : 

Birds, 24.35 Cals. (Zeit. f. Biol., 19, 367). 
Mammals, 24.94 Cals. (ibid., 22, 43). 

(b) Meat fed, 25.98 Cals. (Ibid.). 

(c) Syntonin fed, 26.66 Cals. (ibid.). 

1 grm. carbon in fat, 12.31 Cals. (ibid.). 
f Zeit. f. Biol., 7, 489. 



NET AVAILABLE ENERGY— MAINTENANCE. 



415 



As compared with the fasting state, the 883 Cals. of metaboliz- 
able energy supplied, for example, in 1000 grams of meat diminished 
the loss of energy by the body by 1041 - 250 = 791 Cals. The latter 
quantity, then, represents the extent to which the 883 Cals. supplied 
in the food aided in maintaining the stock of potential energy in the 
body, while the remaining 92 Cals. was consumed in the work of 
digestion and assimilation as defined on previous pages; that is, it 
increased by this amount the heat production of the animal. Ac- 
cordingly we compute that in this case 89.6 per cent, of the metabo- 
lizable energy of the meat was available, while the digestive work 
consumed 10.4 per cent. Computing the other experiments in the 
same way we have — 



Metabolizable 
Energy of 
Food, Cals. 


Gain Over 

Fasting 

Metabolism, 

Cals. 


Net Avail- 
ability, 
Per Cent. 


442 

883 

1325 


510 
791 

1079 


115.4 
89.6 
81.5 



From Rubner's experiments * with proteids (see p. 106) the 
following figures are computed in the same manner as those above : 



Food, 
Grms. 



Metab- 
olizable 
Energy 
of Food, 
Cals. 



Heat 
Produc- 
tion, 
Cals. 



Gain. 



Total, 
Cals. 



Over 
Fasting 
Metab- 
olism, 

Cals. 



Net 
Avail- 
ability, 

Per 
Cent. 



Tem- 
perature, 
Deg. C. 



Meat. 



il 



Extracted meat -j 
Meat 




415 


740 


740 


390 
350 


580 




367 


654 


939 


347 
309 


512 



573* 
596* 
793* 
825* 
931* 
959* 
261f 
334f 
379f 
528f 
681f 



-573 
-229 
-793 
-171 
-931 

- 20 
-261 
-f 13 

- 70 
-528 
-169 



344 
622' 



93.74 



911 

274 
191 

359 



95.15 

97^03 

78.98 
61.80 

70.12 



19.2 
19.6 
18.0 
19.2 
14.9 
15.6 



* Computed. 



f Calorimetric determination. 



* Zeit. f. Biol., 22, 43-48; 30, 117-135. 



416 



PRINCIPLES OF ANIMAL NUTRITION. 



To the above results we may add those of Magnus-Levy's deter- 
minations (p. 381) of the work of digestion and assimilation in the 
dog on a meat diet as follows: 



Proteids Eaten, 


Metabolizable 

Energy of 

Food, 

Cals. 


Expended in 

Digestion and 

Assimilation, 

Cals. 


Net Available. 


Grms. 


Total, 
Cals. 


Per Cent. 


82.5 
230.0 
370.6* 


338 

943 

1520 


56 
116 
244 


282 

827 

1276 


83.43 

87.70 
83.95 



* In excess of maintenance requirements. 

The wide range of the results obtained by Rubner would seem to 
indicate either that the net availability of the energy of the pro- 
teids may vary with different animals and under different conditions 
or that the experimental methods were not sufficiently sharp for the 
purpose now in view. The value of an average drawn from such 
results is questionable, but for the sake of comparison it is included 
below along with those derived from Voit's and Magnus-Levy's 
experiments, Voit's first result being omitted because impossible. 
The figures express the average net availability as a percentage 
of the metabolizable energy. 

Voit's experiments 85 . 60 per cent. 

Rubner's experiments 82.80 " " 

Magnus-Levy's experiments 85 . 03 " " 

Fat. — Computing the results obtained by Pettenkofer & Voit * 
and by Rubner f upon the effects of fat on the total metabolism 
(see pp. 144-146) in the same manner as those upon the proteids, 
and adding Magnus-Levy's results (p. 379), we have the table 
opposite. 

Rubner's and Magnus-Levy's results do not differ widely, and 
their average, 96.4 per cent., indicates a relatively small expendi- 
ture of energy in the digestion and assimilation of fat, which does 
not appear to materially increase above the maintenance require- 
ment. Most of Pettenkofer & Voit's experiments give materially 
lower results above that point, and the one case in which the food 

* Zeit. f. Biol., 5, 370; 7, 440-443; 9, 3-13. 
■flbid., 19, 328-334; 30, 123. 



NET AVAILABLE ENERGY— MAINTENANCE. 



417 



Food. 



Metab- 


Gain. 






olizable 




Over 


Energy 




Fasting 


of Food, 


Total 


Metab- 


Cals. 


Cals. 


olism or 
Basal 

Ration, 
Cals. 





-1086 




942 


-275 


811 


3298 


+ 878 


1964 


442 


-554 




1384 


+ 329 


883 


2326 


+ 837 


1391 





-658 




1738 


+ 1016 


1674 





-373 




356 


-17 


356 





-466 




942 


+428 


894 





-261 




348 


+ 49 


310 





-972 




1250 


+ 259 


1231 





-1055 




2902 


+ 1760 


2815 



Net 
Avail- 
ability, 
Per Cent. 



Pettenkofer & Voit's Experiments : 

Nothing 

100 grms. fat 

350 " fat 

500 " meat 

500 " meat; 100 grms. fat 
500 " " 200 " " 

Rubner's Experiments : 

Nothing 

200 grms. bacon 

Nothing 

39 . 75 grms. butter fat 

Nothing 

100 grms. fat 

Nothing 

40 grms. bacon 

Magnus-Levy's Experiments : 

Fasting 

131 . 6 grms. fat 

Fasting 

305 . 5 grms. fat 



86.1 
59.6 

93.7 

73.8 



98.6 

100. 

94.9 

89.1 

98.5 
97.0 



supply was below the amount required for maintenance also gives 
a rather low availability as compared w th that obtained by the 
other experimenters. 

Carbohydrates. — Tabulating as in the previous cases the re- 
sults of Pettenkofer & Voit * and of Rubner f (see pp. 146-152), 
and adding those of Magnus-Levy (p. 380), we have the figures 
shown on the next page. 

As was the case with fat, most of Pettenkofer & Voit's experi- 
ments give figures notably lower than those obtained by the other 
two investigators. The averages of the latter, omitting the figures 
which exceed 100 per cent., are: 

Rubner's experiments 88 . 9 per cent. 

Magnus-Levy's experiments 91 .0 " " 



* Zeit. f. Biol., 9, 485. 



t Ibid., 19, 357-379; 22, 273. 



4 i8 



PRINCIPLES OF ANIMAL NUTRITION. 



Food. 



Metab- 


Gain. 






olizable 




Over 


Energy 




Fasting 


of Food, 


Total 


Metab- 


Cals. 


Cals. 


olism or 
Basal 

Ration, 
Cals. 





-1098 




2015 


+ 353 


1451 


2661 


-198 


900 


3076 


+ 853 


1951 


442 


-554 




1316 


+ 137 


691 


1180 


+ 108 


662 





-436 




305 


-116 


320 


420 


-22 


414 





-451 




389 


-87 


364 


68 


-374 


77 


572 


+ 190f 


641 





-302 




177 


-138 


164 





-354 




244 


-140 


214 





-302 




702 


+ 365| 


667 


500 


-126 




559 


-84 


42 


691 


+ 34 


160 


2121 


+ 850 


1890 


2226 


+ 934 


2066 


999 


-81 


910 



Net 
Avail- 
ability, 
Per Cent. 



Pettenkofer & Voit's Experiments ; 

Nothing* 

450 grms. starch; 16.9 grms. fat 
597 " " 21.2 " 

700 " " 20.2 " 

500 " meat 

500 " meat; 200 grms. starch 
500 grms. meat; 200 grms. dextrose 

Rubner's Experiments : 

Nothing 

76 . 12 grms. cane-sugar 

104.97 " " " 

Nothing " 

97.3 grms. cane-sugar 

17.0 " " " 

143.0 " " " 

Nothing 

42 . 96 grms. starch (digested) 

Nothing ...... 

57 . 38 grms. starch (digested) 

Nothing 

94 . 36 grms. cane-sugar; 67 . 96 grms. 

starch ; 4 . 7 grms. fat 

300 grms. meat; 63 . 7 grms. dextrose 
300 " " 79.7 " 

300 " " 115.5 " 

Magnus-Levy's Experiments : 

Chiefly rice 1 



72.0 
33.8 
63.4 

79.1 

89.7 



104.9 
98.6 

93.6 
113.2 
112.0 

92.6 

87.8 



95.0 

71.lt 
83. n 



89.1 
92.8 
91.1 



* Fasting metabolism estimated from previous experiments, 
t Gain of carbon assumed to be all in the form of fat. 
% Of dextrose added. 



Experiments on Herbivora. — Comparatively few experiments 
have been reported from which the net availability of the food of 
herbivorous animals can be computed, and as regards the common 
farm animals in particular there is an almost entire lack of data, 
although numerous experiments upon the relative value of various 



NET AVAILABLE ENERGY— MAINTENANCE. 



419 



materials for productive feeding have been reported and will be 
considered in the following chapter. 

Fat. — Rubner's experiments include one * in which fat was 
fed to a rabbit with the following results : 



Metabolizable energy of food . 

Total gain 

Gain over fasting metabolism 
Net availability 



Fasting. 



Cals. 
-101 " 



Fed 26 . 1 Grms. 
Bacon. 



227 Cals. 
+ 122 " 
223 " 
98.2$ 



In connection with his investigations upon cellulose, v. Knie- 
riem f also experimented upon the influence of fat on the metabo- 
lism of the rabbit. The basal ration consisted of milk, to which 
was added in the second period 3.94 grams of dry butter fat per day. 
Computing the amounts of energy by the use of Rubner's factors 
the results were : 





Metabolizable 
Energy, Cals. 


Gain, Cals. 


Net Availability, 
Per Cent. 


Milk and butter fat 


207.3 
169.8 


-19.5 
-55.2 




Milk 




Difference 


37.5 


35.7 


95.2 



Carbohydrates. — Rubner % reports three experiments with 
cane-sugar on a cock from which the following results are com- 
puted : 



Food. 



Metaboliz- 
able Energy 
of Food, 
Cals. 



Gain. 



Total, 
Cals. 



Over Fast- 
ing Metab- 
olism, Cals. 



Net 

Availability, 

Per Cent. 



Nothing 

34 grms. cane-sugar 

Nothing 

45 grms. cane-sugar 
50 " 




136 


180 
200 



-239 
-121 
-258 
-101 
- 53 



118 

157 

205 



86.8 

87.2 
102.5 



* Zeit. f. Biol., 19, 333. 



t Ibid., 21, 119. X Ibid., 19, 366. 



420 



PRINCIPLES OF ANIMAL NUTRITION. 



From the comparisons of cellulose and cane-sugar made by v. 
Knieriem (loc. cit.) and cited on p. 161, the following figures for the 
net availability of the energy of the latter substance may be com- 
puted : 



49 

a 


CO 


6 


Food per Day. 


Metab- 
olizable 
Energy 
of Food, 
Cals. 


Gain. 


Net 


J 

& 


Total, 
Cals. 


Over 

Basal 

Ration, 

Cals. 


Avail- 
ability, 
Per Cent. 


III 


5 
4 
3 


Milk.. . , 


350.1 
393.7 
480.7 


-37.9 
-15.9 
+ 69.9 


22.0 
107.8 




IV 
V 


" + 1 1 grms. cane-sugar . . 
" +33 " " " .. 


50.5 

82.5 



A series of experiments by May * upon the effect of fever on 
metabolism affords incidentally a few data bearing on the availa- 
bility of the energy of dextrose. In his experiment No. 5 (loc. cit., 
p. 23) the ingestion of 30 grams of grape-sugar, an amount approxi- 
mately equivalent to the fasting metabolism, caused no increase in 
the computed heat production as compared with that during fasting. 
In this experiment there was no fever. In Experiment No. 6 (p. 25), 
with fever, the ingestion of the same amount of grape-sugar pro- 
duced a computed gain of 2.88 grams carbon as fat, but caused no 
increase in the computed heat production. Experiment No. 7 
(p. 26) was similar to No. 6, but showed a decrease in the computed 
heat production, which, however, coincided with a decrease in the 
fever. On the whole, May's results appear in accord with Rubner's 
hypothesis of a substitution of the heat resulting from digestive 
work for that arising from the metabolism of tissue. 

Pentoses. — Cremer's experiments f with rhamnose upon rabbits, 
cited in Part I, p. 157, afford data for computing the net availa- 
bility of this representative of the pentoses. For this purpose 
Cremer computes from the excretion of nitrogen and carbon (neg- 
lecting the feces), in the manner described in Chapter VIII, p. 253, 
the amount of energy liberated by the metabolism of protein and 
fat in the body, assuming that the rhamnose, after deducting the 
small amounts in feces and urine, was completely oxidized. The 
following are the results for each day of the four experiments: 



* Zeit. f. Biol., 30, 1. 



f Ibid., 42, 451. 



NET AVAILABLE ENERGY— MAINTENANCE. 



421 



Food, Grms. 


Metabolizable 
Energy of Food , 

Cals. 


Loss by Body, 
Cals. 


Experiment I : 

Nothing 




45.3 





66.8 





74.1 








72.9 
22.0 


147.4 
114.0 
113.3 

180.7 
111.6 

184.8 

129.1 

54.3 

113.1 

113.4 

146.0 

141.4 

53.3 

98.1 


Rhamnose, 11 .584 grms. . . . 
Nothing 


Experiment II : 

Nothing 


Rhamnose, 17.09 grms 

Nothing 


Experiment III : 

Nothing 


Rhamnose, 18 . 96 grms 

Nothing 


" (av'ge of two days) 

Experiment IV : 

Nothing 




Rhamnose, 18 . 66 grms 

5.64* " 



* The total amount of rhamnose (24 . 3 grms.) was given on the first day, 
but it is estimated from the results for the carbon excretion that this amount 
of it was not metabolized until the second day. 

The results as to net availability obtained by comparison with 
the several fasting days vary considerably, as the following state- 
ment shows, several of them exceeding 100 per cent. : 

Experiment I. 

Compared with first day 74 per cent. 

" " third day Negative 

Experiment II. 

Compared with first day 103 per cent. 

" " third day 110 " " 

Experiment III. 

Compared with first day 101 per cent. 

" third day 79 " " 

Second and third with fourth and fifth days. 80 " " 

Experiment IV. 

Third compared with second day 121 per cent. 

" " " fourth day 88 " " 



422 



PRINCIPLES OF ANIMAL NUTRITION. 



The great variations in the results, as well as the large propor- 
tion of cases in which the availability appears to exceed 100 per 
cent., show that little value attaches to them as quantitative deter- 
minations, although they undoubtedly show that rhamnose pos- 
sesses a comparatively high nutritive value. 

Crude Fiber. — The experiments of v. Knieriem have already 
been cited in Chapter V in their general bearings upon the metabo- 
lism of matter. As was there noted, certain corrections were neces- 
sary on account of the residue of undigested cellulose remaining 
in the digestive canal at the close of the experiment. The results 
given below are based on those computed by the author, as sum- 
marized on p. 161, on the assumption that the resorption of the 
remaining digestible crude fiber was complete after two days. 





>> 

Q 



d 


Food per Day. 


Metab- 
olizable 
Energy 
of Food, 
Cals. 


Gain. 


Net 


.2 

IK 
Ph 


Total, 
Cals. 


Over 

Basal 

Ration, 

Cals. 


Avail- 
ability, 
Per Cent. 


T 


9 
10 

5 


Milk 


341.7 
374.6 
350.1 


-46.8 
- 6.9 | 
-37.9 


39.9 
31.0 




II 
TTT 


" + 22grms. crude fiber | 

for eight days j 

Milk 


121.3* 
126. 5f 









* Compared with Period I. 



f Compared with Period III. 



It is evident from the above figures that while the experiments 
show qualitatively a nutritive value for the cellulose, they are in- 
sufficient for a quantitative determination of its amount. 

In striking contrast with these results are the conclusions drawn 
by Zuntz & Hagemann from their experiments upon the horse 
which have already been considered in the previous chapter (pp. 
389-391). As was there explained in detail, these investigators 
have estimated the expenditure of energy in the digestion of crude 
fiber from a comparison of the computed heat production in two 
sets of experiments in which the proportion of coarse fodder eaten 
differed considerably, it being assumed that 9 per cent, of the metab- 
olizable energy of the nutrients other than crude fiber was consumed 
in their digestion. On this basis the digestive work caused by the 
crude fiber is computed at 2.086 Cals. per gram, or rather more than 



NET AVAILABLE ENERGY— MAINTENANCE. 423 

its average metabolizable energy. In other words, it is computed 
that under the conditions of these experiments, with a ration more 
than sufficient for maintenance, the net availability of the energy 
of the crude fiber was practically zero. The authors report no 
experiments upon rations below the maintenance requirement, but 
appear to regard the metabolizable energy of the crude fiber as being 
indirectly available, under such conditions, substantially in the 
manner assumed by Rubner and already explained. 

As has been noted, Zuntz & Hagemann's conclusions as to the 
value of crude fiber for work production are in apparent harmony 
with those of Wolff, which will be discussed in the next chapter, but 
on the other hand they contrast sharply with the results of Kellner 
(see Chapter XIII, § 1), who observed a high percentage utilization 
of the energy of one form of crude fiber in the ration of fatten- 
ing cattle. On previous pages some reasons were presented for 
questioning the quantitative accuracy of Zuntz & Hagemann's 
computations, but even aside from these their conclusions as re- 
gards the value of crude fiber are difficult to reconcile with obvious 
facts. Thus they compute (loc. cit., p. 280) that the expenditure 
of energy in the mastication and digestion of average straw is 
greater than its metabolizable energy, so that for the horse this 
material has a negative value. When forming part of a mainte- 
nance ration we m^y probably assume that below the critical 
amount of food (p. 408) the heat generated during the digestion of 
the straw would be of use to maintain the body temperature, but 
this could not possibly suspend the expenditure of energy in the 
various forms of internal work, such as respiration and circulation. 
Since, however, by hypothesis, the straw can contribute no energy 
directly for these purposes, it follows that the consumption of this 
material alone cannot reduce the loss of tissue below the amount 
requisite to supply energy for the internal work, while on an 
exclusive straw ration above the critical amount of food the more 
straw the animal consumed the sooner it would starve. 

Organic Acids.— The results of a considerable number of ex- 
periments in which salts of organic acids were mjected into the 
blood have already been presented in Chapter V (p. 157). The 
general result was that lactic and butyric acids caused little or 
no increase in the heat production of the animal — in other words 



424 



PRINCIPLES OF ANIMAL NUTRITION. 



that practically all their potential energy was available to prevent 
loss of tissue. In such experiments, of course, there is no digestive 
work in the proper sense. What they indicate is that what we 
have called rather loosely the work of assimilation for these sub- 
stances is practically zero. Acetic acid, on the other hand, was 
found by Mallevre to increase the consumption of oxygen by from 
10 to 17 per cent., indicating a considerable waste of energy directly 
or indirectly. The general nature of these experiments is not such, 
however, as to afford data of much direct value in relation to the 
question of the availability of the energy of ordinary foods. 

Timothy Hay. — The experiments described in the foregoing 
paragraphs relate to pure or nearly pure nutrients. Experiments 
upon a steer have been made by the writer in conjunction with 
Fries in which the availability of the apparent metabolizable energy 
of timothy hay has been determined. To a basal ration consider- 
ably below the maintenance requirement, consisting of 3250 grams 
of hay and 400 grams of linseed meal, three different additions of 
timothy hay were made, the digestibility of the ration in each 
period being determined, and likewise the total balance of nitrogen, 
carbon, and energy by means of the respiration-calorimeter. The 
results as to energy, uncorrected for the very small differences in 
the organic matter of the basal ration consumed and for the 
changes in the live weight of the animal, were as follows : * 



Period A. 



Outgo, 
Cals. 



Income, 
Cals. 



Period B. 



Outgo, 
Cals. 



Income, 
Cals. 



Period C. 



Outgo, 
Cals. 



Income, 

Cals. 



Period D. 



Outgo, 
Cals. 



Income, 
Cals. 



Feed 

Excreta : 

Feces 

Urine 

Methane . . . 
Metabolizable 



Metabolizable . 
Heat produced 
Gain or loss. . . . 



14,923 



20,297 



25,198 



29,647 



6,446 
863 
996 

6,618 



8,590 

974 

1,251 

9,482 



11,477 
1,125 
1,374 

11,222 



14,276 
1,220 
1,896 

12,255 



14,923 



9,067 



14,923 
6,618 



20,297 



10,206 



20,297 
9,482 



25,198 



2,449 



724 



10,606 
616 



25,198 
11,222 



29,647 



11,183 
1,072 



9,067 



9,067 



10,206 



10,206 



11,222 11,222 



12,255 



29,647 
12,255 

12,255 



* Proc. Soc. Prom. Agr. Sci., 1902. 



NET AVAILABLE ENERGY—MAINTENANCE. 



4 2 5 



Subtracting the results on the basal ration of Period A from those 
of the other periods, as in previous cases, we have the following : 





Metabolizable 

Energy, 

Cals. 


Gain of Tissue, 
Cals. 


Net Availability, 
Per Cent. 


Period B 


9,482 
6,618 


-724 
-2,449 




A 




Difference 


2,864 

11,222 
6,618 


1,725 

616 
-2,449 


60 24 


Period C 

A 








Difference 


4,604 

12,255 

6,618 


3,065 

1,072 
-2,249 


66 57 


Period D 




A 




Difference 


5,637 


3,521 


62.46 


Average 


63 09 











Strictly speaking, only the first of the above percentages repre- 
sents the net availability for maintenance, since the other two 
include some gain. From the difference observed between the 
metabolism of the animal standing and lying, however, it was 
computed approximately what the gains would have been had the 
same position been maintained for the whole twenty-four hours, 
with the following results: 





Metabolizable 
Energy, Cals. 


Gain, Standing, 
Cals. 


Net Availability, 
Per Cent. 


Period B 


9,482 
6,618 


-1,606 
-3,507 




" A 








Difference 


2,864 

11,222 

6,618 


1,901 

-550 
-3,507 


66.37 


Period C 




" A 








Difference 


4,604 

12,255 
6,618 


2,957 

23 

-3,507 


64.23 


Period D 




" A 








Difference 


5,637 


3,530 


62.62 






Average 


64.41 











426 



PRINCIPLES OF ANIMAL NUTRITION. 





Metabolizable 
Energy, Cals. 


Gain, Lying, 
Cals. 


Net Availability, 
Per Cent. 


Period B 


9,482 
6,618 


1,157 
-1,046 




" A 








Difference 


2,864 

11,222 

6,618 


2,203 

2,136 
-1,046 


76 92 


Period C 




" A 








Difference 


4,604 

12,255 
6,618 


3,182 

2,743 
-1,046 


69 12 


Period D 




" A 








Difference 


5,637 


3,789 


67.22 


Average 


71 08 











The results are likewise shown graphically on the accompanying 
diagram, in which the full line represents the average availability 



3000 



2000 



1000 



-1000 



-2000 



-3000 



-4000 




7000 



8000 9000 10000 11000 

METABOLIZABLE ENERGY, CALS. 



12000 



NET AVAILABLE ENERGY— MAINTENANCE. 



427 



observed and the broken lines that computed respectively for 
standing and lying, while the points indicate the results for each 
period. As computed standing, the results are all practically at or 
below the maintenance point, and their fairly close agreement with 
each other and with those actually observed indicates that the net 
availability of the metabolizable energy of this sample of timothy 
hay was between 63 and 65 per cent. 

Summary. — The foregoing data as to availability are sum- 
marized in the following table, those experiments in which the total 
ration was less than the maintenance requirement being separated 
from those in which more or less gain by the body took place : 



Experiments on Carnivora. 
Below Maintenance. 
Proteids : 



Pettenkofer & Voit 



Rubner . 



Magnus-Levy 



PerCent. 
115.4 
89.6 
93.7 
95.2 
97.0 
61.8 
70.1 
83.4 
87.7 



Fat: 

Pettenkofer & Voit 86 . 1 

Rubner 100.0 

Starch : 

Pettenkofer & Voit 33 . 8 

92.6 
87.8 

Magnus-Levy (rice) 91.1 



Rubner . 



Dextrose : 

Rubner 71.3 



Experiments on Herbivora. 
Below Maintenance. 



Fat : Per Cent, 
v. Knieriem 95.2 




Starch and Cane-sugar : 

Rubner 95.0 



428 



PRINCIPLES OF ANIMAL NUTRITION. 



Pentoses 



Cremer 



Crude Fiber: 
v. Knieriem. 



Timothy Hay: 
Armsby & Fries 

Above Maintenance. Above Maintenance. 

Proteids : Per Cent. 

Pettenkofer & Voit 81.5 

Rubner 79.0 

Magnus-Levy 84 . 

Fat: ^t: 

i 59 . 6 Rubner 

Pettenkofer & Voit ] 93 . 7 

( 73.8 

t 98.6 

Rubner •! 94.9 

I 89.1 

T i 985 

Magnus-Levy -j Q7 Q 

Starch : 

i 72.0 

Pettenkofer & Voit ) 63 .4 

( 79.1 

Magnus-Levy (rice) j ^ ' 

Dextrose : 

Pettenkofer & Voit 89 . 7 

Rubner 83.7 

Cane-sugar : Cane-sugar : 

Rubner 112 . v. Knieriem 

Cane-sugar and Starch : 

Rubner 95.0 



74.0 

(?) 
103.0 
110.0 
101.0 

79.0 

80.0 
121.0 

88.0 

121.3 
126.5 



63-65 



Per Cent. 
. 98.2 



82.5 



NET AVAILABLE ENERGY— MAINTENANCE. 429 

It scarcely seems possible to draw any well-founded conclusions 
regarding the net availability of the several nutrients from such 
widely divergent results as those tabulated above, even if the ex- 
treme and obviously incorrect figures be discarded. Two things, 
however, seem worthy of remark. 

First, in but few cases does the net availability of the food reach 
100 per cent., and most of those results relate to cane-sugar or rham- 
nose ; that is, to cases in which some of the gain of carbon which is 
computed as fat may have been in the form of a carbohydrate. It 
would seem fairly safe to conclude, therefore, that no such complete 
substitution of the heat resulting from digestive work for that re- 
sulting from the general metabolism took place as Rubner's hypoth- 
esis supposes. Apparently, under the conditions of these experi- 
ments, there was, in most cases at least, a material loss of energy 
in digestive work. 

Second, there is no clear indication of a smaller loss of energy 
below than above the maintenance ration, although the wide range 
of the results renders a definite conclusion upon this point hazardous. 
This question, however, may be more properly considered in con- 
nection with a study of the utilization of the net available energy of 
the food. 

Finally, it is to be said that if the validity of the conception of 
a critical amount of food, as developed on p. 409, be admitted — 
that is, of an amount of food below which the heat resulting from 
the work of digestion and assimilation is substituted for that pro- 
duced by the general metabolism, while above it no such substitu- 
tion takes place — a very important element is lacking for the 
interpretation of the above experiments, except, perhaps, those on 
timothy hay, in which the uniformity of the results with varying 
amounts seems to show clearly that all the rations supplied more 
than the critical amount of food. If that conception is correct, 
to determine the real availability of the energy of a food it is 
necessary to compare the effects of two quantities both of which 
are greater than the critical amount. On the other hand, the 
complete substitution of energy supposed by Rubner could only 
be demonstrated by comparing quantities less than the critical 
amount, while a comparison of quantities below the latter 
amount (including, of course, fasting) with those exceeding it 



43° PRINCIPLES OF ANIMAL NUTRITION. 

can give only mixed results varying with the quantities com- 
pared. 

It seems tolerably clear, then, that the whole subject of the net 
availability of foods and nutrients needs reinvestigation by more 
rigorous methods and with due regard to the amounts of the food 
materials compared and to the thermal environment of the animals 
experimented upon. 

Discussion of Results. 

For the reasons just stated, any strict quantitative discussion 
of the above results seems impossible. At the same time, certain 
general conclusions may be at least tentatively deduced from them 
which, even though to a considerable extent speculative, may at 
least serve provisionally as a connecting thread between the known 
facts. 

Influence of Amount of Food on Availability. — In the fore- 
going paragraphs it has been tacitly assumed that the amount of 
food eaten has no influence on its availability, or, to state it in 
another way, that the expenditure of energy in digestion and assimi- 
lation is proportional to the quantity of food. To express the same 
thing in mathematical terms, we have assumed, in constructing the 
• diagram on p. 410, that the net available energy is a linear function 
of the metabolizable energy. 

While it seems highly probable that such is the case the only ex- 
periments bearing specifically upon this question of which the writer 
is aware are those upon timothy hay just cited. An examination 
of the graphic representation of the results strongly supports the 
hypothesis that the net availability of the food is independent of 
its amount, but the evidence of so few experiments must naturally 
be accepted with some reserve. The other recorded results, as 
computed above, apart from the possible source of uncertainty 
pointed out on p. 429, show such considerable variations in indi- 
vidual cases that it scarcely seems possible to reach any definite 
conclusions from them regarding the influence of quantity of food. 
As will appear in the next chapter, the extensive respiration exper- 
iments made in recent years at the Mockern Experiment Station by 
G. Kiihn and 0. Kellner upon fattening cattle indicate that the 



NET AVAILABLE ENERGY— MAINTENANCE. 43 1 

actual gain obtained (expressed in terms of energy), at least within 
certain limits, is proportional to the amount of metabolizable energy 
supplied in excess of maintenance. This would mean that above 
the maintenance ration the energy required for digestion and 
assimilation plus that consumed in the chemical changes incident 
to the formation of new tissue (compare p. 396) is proportional 
to the amount of food. If this be true it seems more reasonable 
to conclude that each of these forms of work separately is propor- 
tional to the amount of food than to assume a compensation between 
the two, and granting this, we should have every reason to suppose 
that the same proportionality would hold good for the work of 
digestion and assimilation below the maintenance requirement. 

Character of Food. — The investigations of Zuntz & Hagemann 
(pp. 385-393) have shown that, in the case of the horse at least 
and doubtless with other animals also, the work of digestion and 
assimilation varies with the kind of food, a result which is entirely 
in accordance with what we should expect. For reasons stated in 
describing their experiments, their results are to be regarded as 
qualitative rather than quantitative, but they suffice to demon- 
strate the very marked difference as regards availability which 
exists between the relatively pure nutrients employed in the exper- 
iments of Pettenkofer & Voit, Magnus-Levy, Rubner, and others 
and the feeding-stuffs consumed by our herbivorous domestic 
animals, and to show the fallacy involved in applying the results 
of the former experiments directly to the latter case. The same 
conclusion is also indicated by the few results upon timothy hay 
on p. 424. 

Unfortunately no other direct determinations of the availability 
of the food of herbivorous animals in amounts below the mainte- 
nance ration are on record, so that we are unable to compare either 
different feeding-stuffs or different species of animals in this respect. 
The extensive investigations of the Mockern Experiment Station 
mentioned in the previous paragraph show how large a proportion 
of the metabolizable energy of the food of fattening animals becomes 
economically waste energy, thus fully confirming the conclusions 
drawn from Zuntz & Hagemann's experiments upon the horse, but 
they afford no means of distinguishing between the work of diges- 



43 2 PRINCIPLES OF ANIMAL NUTRITION. 

tion and assimilation and the energy expended in converting the 
resorbed material into permanent tissue. 

The Maintenance Ration. — As already defined, net available 
energy is that portion of the metabolizable energy of the food 
which serves to make good the losses of potential energy arising 
from the internal work plus the work of digestion and assimilation, 
or, in other words, which contributes towards the maintenance of 
the stored-up capital of energy. We may, therefore, appropriately 
consider the bearings of the known facts regarding availability 
upon the amount of food required for maintenance. 

Relations to Availability. — Not a little effort has been 
expended in determining the maintenance requirements of farm 
animals on the more or less tacit assumption that this quantity is 
a constant for the same animal, and the same assumption has even 
more largely controlled in computations based on the experimental 
data obtained. 

By the maintenance ration, of course, we understand a ration 
just sufficient to prevent any loss of tissue — that is, of potential 
energy — by the animal. To accomplish this we must give a ration 
containing net available energy equal in amount to the potential 
energy lost when no food is given. Expressed thus in terms of net 
available energy, the maintenance requirement under given condi- 
tions is a constant and is equal to the energy of the fasting metabo- 
lism. 

The maintenance requirement, however, particularly in the case 
of farm animals, has not usually been expressed thus, since the 
necessary data are lacking, but in terms of total digestible matter 
or of real or supposed metabolizable energy. When thus expressed, 
however, it is apparent in the light of the foregoing discussion that 
the maintenance requirement must be a variable, depending upon 
the availability of the metabolizable energy of the food. Referring 
again to the graphic representation on p. 410, it is evident that, 
under the conditions there represented, with an availability ex- 
pressed by tan DAC, the amount of metabolizable energy required 
for maintenance will be equal to OS. Furthermore, it is equally 
evident that as the availability decreases and the angle DAC con- 
sequently becomes more acute OS will increase. Only when the 
critical amount of food, OM, is greater than the fasting metabolism 



NET AVAILABLE ENERGY— MAINTENANCE. 433 

and the point K falls above the axis OX will there be an apparent 
exception to this law. In that case, since the energy expended in 
digestion and assimilation seems to be indirectly utilized, the ap- 
parent availability will be 100 per cent, and the metabolizable 
energy required for maintenance will be constant and equal to the 
energy of the fasting metabolism. 

This case might and perhaps does occur with animals whose food 
consumes little energy in digestion, such as the carnivora. As was 
pointed out on p. 412, however, an increase in the work of digestion 
tends to reduce the critical amount of food and there would appear 
to be good reason for believing that, in ruminants at least if not in 
the horse, it lies considerably below the point of maintenance. 

Relative Value of Grain and Coarse Fodder. — We know 
from the investigations of Zuntz & Hagemann (pp. 385-393) that 
the work expended in the digestion of coarse fodders is, in the horse 
and presumably therefore in other animals, materially greater than 
that caused by grain. It follows, then, that a unit of digestible 
matter or of metabolizable energy should have more value for 
maintenance in the latter than in the former. 

That such is the case with cattle is rendered probable by experi- 
ments by the writer.* In the absence of a respiration apparatus 
the nutritive effect of the rations was judged of from the live weight 
and the proteid metabolism during relatively long periods and the 
methane production was computed from the carbohydrates digested. 
A ration in which only about 24 per cent, of the digested organic 
matter was derived from coarse fodder, as compared with rations 
consisting exclusively of coarse fodder, gave the following results 
for the metabolizable energy of the maintenance ration per day 
and 500 kgs. live weight: 

Exclusive coarse fodder, 12 experiments. . . . 12,771 Cals. 
Largely grain, 3 experiments 11,023 

Such determinations of the maintenance requirements of the 
horse as have been made tend to confirm the results obtained with 
ruminants. Wolff, in his investigations upon work production 
described in the following chapter, has computed the maintenance 
requirements of the horse in the manner there explained both from 

* Penna. Expt. Station, Bull. 42, p. 159. 



434 PRINCIPLES OF ANIMAL NUTRITION. 

his own experiments and from those of Grandeau and LeClerc, 
with the following results per 500 kgs. live weight : 

Total Digestible Nutrients,* 
Grms. 

On hay alone 4586 

About equal parts hay and grain 4190 

About f grain and \ hay (Grandeau) 3626 

Zuntz & Hagemann,f from the results of a respiration experi- 
ment with the horse, make a still lower estimate of the maintenance 
requirement, viz., 3265 grams total nutrients per 500 kgs. live 
weight on a ration of which about four sevenths was grain, but 
after allowing for the differences in crude fiber content compute a 
satisfactory agreement between their results and Wolff's. Since 
their estimate for the work of digestion of crude fiber is really 
based on the difference in digestive work required by coarse fodder 
and by grain this is equivalent to showing that the latter is more 
valuable for maintenance than the former. 

On the other hand, Grandeau and LeClerc % in later experiments 
on exclusive hay feeding found that the live weight was almost 
exactly maintained for a month on 8 kgs. of hay per day, the total 
digested nutrients being as follows: 



Animal. 


Live Weight, 
Kgs. 


Total Digestible Nutrients. 


Per Head, 

Grms. 


Per 500 Kgs., 
Grms. 


No. 1 


395 
419 

413 


2892 
3036 
3058 


3660 
3622 
3701 


" 2 


" 3 





These figures do not materially exceed the average computed by 
Wolff from their previous experiments on heavy grain rations. The 
horses had a half-hour's walking exercise daily, so that the ration 
seems to have been amply sufficient for maintenance, and no reason 
for the divergent result is obvious. 

While none of these comparisons have the conclusiveness of 

* Including fat X 2.4. 

t Loc. tit., pp. 422-4. 

^ L' alimentation du Cheval du Trait, 3d memoir, pp. 23-31. 



NET AVAILABLE ENERGY— MAINTENANCE. 435 

complete metabolism experiments, their results as a whole indicate 
clearly that the metabolizable energy of the grains is more valu- 
able for maintenance than that of the coarse fodders, a fact un- 
doubtedly due to the greater expenditure of energy in the digestion 
and assimilation of the latter. 

The maintenance ration of horses, cattle, and sheep, then, as 
ordinarily expressed (i.e., in units of digestible matter or of metabo- 
lizable energy) is not a constant but a variable, depending on the 
availability of the metabolizable energy, and such a statement of it, 
to be definite, must be accompanied by a statement of the kind of 
feed used. 

No similar experiments upon swine appear to have been made. 
The ordinary feed of this animal, however, probably varies less in 
availability than that of ruminants, and it may be presumed that 
no such striking differences would be found. 

Value of Crude Fiber. — As a result of Wolff's conclusions con- 
cerning the apparent worthlessness of crude fiber for work production, 
as discussed in the succeeding chapter, and of Zuntz & Hagemann's 
estimates regarding its digestive work (p. 389), there has been a 
tendency to ascribe the difference between grain and coarse fodders 
to the greater amount of crude fiber in the latter, forgetting that 
what these investigators have actually shown is simply the lower 
value of the digestible matter from coarse fodders, and that their 
conclusions regarding crude fiber are deductions from the observed 
facts. Kellner's more recent experiments (see p. 182 and Chapter 
XIII, § 1) have demonstrated that at least one form of crude fiber 
is nearly as efficient in producing a gain of fat by cattle as is 
starch. A fortiori, therefore, it should be equally valuable for 
maintenance. We have as yet no sufficient evidence to justify us 
in ascribing the difference between grain and coarse fodder to the 
crude fiber as such aside from its influence on the mechanical 
structure of the material. 

Influence of Thermal Environment. — It has been not 
uncommonly assumed that the maintenance requirement of an 
animal is affected by changes in the temperature and other external 
factors which combine to determine the refrigerating effect of the 
environment; in other words, the heat production of the animal 
has been looked upon more or less distinctly as an end in itself. 



43 6 PRINCIPLES OF ANIMAL NUTRITION. 

We have already seen reason to believe that this is the case to a 
very limited extent only, even in the fasting animal, and to a still less 
degree in one consuming food. If we are justified in thinking that 
the critical amount of food for herbivorous animals is ordinarily 
less than the maintenance requirement, it follows that the heat 
production on a maintenance ration is in excess of the actual needs 
of the organism for heat by an amount depending upon the avail- 
ability of the metabolizable energy of the food, and that this excess 
of heat is disposed of by "physical" regulation. That such is the 
case appears to be clearly indicated by the writer's experiments 
upon timothy hay (p. 424), since there was obviously no such in- 
direct utilization of the heat resulting from the work of digestion 
and assimilation as takes place, according to Rubner's theory, 
below the critical amount of food. If, now, the temperature to 
which such an animal is exposed falls, it is in accord with all that 
we know regarding the regulative processes in the body to suppose 
that the additional draft on it for heat will be compensated for by 
a fall in the emission constant rather than by an increased produc- 
tion of heat, or, to put it in another way, that some of the heat 
resulting from digestive work will be utilized to maintain the tem- 
perature of the animal instead of being at once dissipated. 

No exact experiments upon the influence of external tempera- 
ture on the maintenance requirement appear to have been made, 
but Kern, Wattenberg & Pfeiffer * have investigated the influence 
of the greater exposure to cold caused by shearing upon the metabo- 
lism of sheep consuming a maintenance ration. A slight decrease 
in the proteid metabolism was found to result, due, as Pfeiffer con- 
jectures, to a more rapid growth of wool after shearing, but the 
corresponding difference in the metabolism of energy is insignificant. 
The removal of a nine-months fleece appears to have caused at first 
an increased excretion of carbon dioxide, but this practically dis- 
appeared within four or five days and is probably to be attributed 
to greater muscular activity on the part of the shorn animals. 
Comparing the results before shearing with those obtained from 
five to sixteen days after, we have the following averages, the 
amount of water-vapor given off being only an approximate esti- 
mate: 

* Jour, f . Landw., 39, 1. 



NET AVAILABLE ENERGY— MAINTENANCE. 437 





Carbon dioxide 

per Day, 

Grms. 


Estimated 

Water -vapor 

per Day, 

Grms. 


Before shearing (4 experiments) . . . 
After " (4 " ) . . . 


719.6 

725.1 


1939 
434 



The total metabolism, as indicated by the excretion of carbon 
dioxide, shows scarcely any increase as a result of the shearing, and 
if we accept Pfeiffer's suggestion that the result for the first of the 
four days (736 grams) may have been slightly affected by the stimu- 
lation of movement above noted, the difference becomes still less. 
On the other hand, the difference in the amount of water-vapor 
given off is very striking and apparently admits of but one con- 
clusion, viz., that drawn by Pfeiffer, that the unshorn animals upon 
a maintenance ration produced an excess of heat which was gotten 
rid of by evaporation of water, while the shorn animals, instead of 
meeting the greater refrigerating effect of their surroundings by an 
increased metabolism, simply evaporated less water and thus com- 
pensated for the increased loss of heat by radiation and conduction. 

Even in the case of man, where the digestive work is much 
less than in the herbivora, the heat production on a mainte- 
nance ration may be in excess, and even largely in excess, of the 
minimum requirement, it being simply a question of clothing, 
temperature, etc. This has been most strikingly demonstrated 
by Ranke,* who shows that with relatively high temperature and 
humidity the heat production on a maintenance ration may be so- 
great as to even produce pathological effects and that under such 
circumstances the consumption of food is instinctively reduced 
below the maintenance requirement. 

Sanborn,f in experiments upon the maintenance ration of swine, 
found the amount of middlings required, per hundred pounds of live 
weight, to be as tabulated on the next page. The second summer 
experiment is not comparable with the others, since the smaller 
animal would require a relatively greater maintenance ration. 
The remaining experiments seem to show a lower requirement for 
maintenance in winter than in summer. 

* Einfluss des Tropenklimas auf die Ernahrung des Menschen, and Zeit. 
f. Biol., 40, 288. 

f Mo. State Agr. Coll., Bull. 28, pp. 5 and 6. 



43§ 



PRINCIPLES OF ANIMAL NUTRITION. 





Live Weight, 
Lbs. 


Maintenance 

Requirement, 

per 100 Pounds, 

Lbs. 


Winter (temp, about 40° F.) ... . | 
Summer ( " " 80° F.) .... -j 


173.5 

171.6 

173.6 

48.3 


1.65 
1.89 
2.02 
2.07 



On the other hand, Cooke,* in a series of experiments on swine 
at the Colorado Station, found the following amounts of computed 
digestible matter required for maintenance per hundred pounds live 
weight of animals weighing from 85 to 182 pounds per head : 

In hot weather . 93 lbs. 

In moderate weather 1 . 25 " 

In cold weather 1.41 " 

Consumption of Water. — A not inconsiderable amount of energy 
is usually required to raise the ingesta to the temperature of the 
body. This is particularly true of the water consumed, especially 
in case of the herbivora, both by reason of its relatively large amount 
as compared with the dry matter of the food and on account of its 
high specific heat. At first thought it might seem that the warming 
of the ingesta is part of the work of digestion, since it is an expendi- 
ture of energy in preparing the food for assimilation. This same 
matter or its equivalent, however, finalhy leaves the body, in the 
form of various excreta, at body temperature, thus carrying off as 
sensible heat substantially the same amount of energy which was 
imparted to it when its temperature was raised, and this heat it 
imparts in cooling to the environment of the animal. It would 
seem, then, that the warming of the ingesta may be more logically 
regarded as a part of the general draft for heat which the surround- 
ings make upon the animal, the process being simply a little less 
direct than the loss of heat by radiation and conduction through 
the skin. 

From this point of view the influence of the consumption of cold 

food and particularly of cold water will be subject to the same 

general laws as the other forms of the demand for heat. On a 

ration supplying less than the critical amount of metabolizable 

* Private communication. 



NET AVAILABLE ENERGY— MAINTENANCE. 439 

energy any increase in the consumption of water (taking this as the 
typical case) will increase the metabolism by an amount sufficient 
to warm the water to the body temperature. Above the critical 
amount of food the excess of heat arising from the digestive work 
will, we may reasonably suppose, be applied to the warming of the 
additional water consumed, and only when this is insufficient will 
an increased metabolism be required to make up the deficit. In 
case of farm animals, however, it would appear that the waste heat 
even on a maintenance ration is ordinarily sufficient, and more 
than sufficient, to supply all the energy needed for warming the 
ingesta. 

The Time Element. — One important factor in modifying the 
results of the demand for heat, particularly with relation to the 
water consumption, is what we may call the time element. Hitherto 
it has been tacitly assumed that all the factors making up the 
demand for heat act at a uniform rate. As a matter of fact this is at 
best only partially true. Ordinarily a farm animal is watered but 
■once or twice per day and then consumes a relatively large amount 
In a few minutes. A sudden demand for heat is thus set up, since 
this water must be raised to body temperature within a compara- 
tively short time. It is quite conceivable, therefore, that the demand 
for heat may temporarily exceed the supply, requiring the deficit 
to be made up by an increased metabolism, while if the same water 
consumption were distributed uniformly over the twelve or twenty- 
four hours no such effect would be produced. Such a temporary 
increase in the heat production, however, cannot be made up for 
later when the heat production is in excess, but is a permanent loss. 
Once converted into heat, the energy of food or tissue has, so to 
speak, escaped from the grasp of the organism, which appears to 
have no power to reconvert it into any other form of energy. We 
may plausibly suppose that these considerations constitute a partial 
explanation of the advantages observed in practice from the warm- 
ing of drinking-water and the installation of self-watering devices 
in the stable. 

What is true in regard to the consumption of water is of course 
equally true of other forms of the demand for heat. The time ele- 
ment is an important factor. Thus an exposure of an hour or two 
in a cold yard or to a cold rain may cause an increased metabolism 



44° - PRINCIPLES OF ANIMAL NUTRITION. 

and heat production although the average conditions for the twenty- 
four hours may be such that the necessary production of heat by 
the internal work and the work of digestion and assimilation would 
be more than sufficient for the needs of the animal. 

Influence of Size of Animal. — The discussion of the heat 
production of the fasting animal in Chapter XI led us to the con- 
clusion that under comparable conditions, at least for the same 
species of animal, the internal work is probably approximately 
proportional to the surface of the body. This, however, is equiva- 
lent to saying that the quantity of net available energy required 
for maintenance is proportional to the body surface. Furthermore, 
if we are right in supposing that the available energy is a linear 
function of the metabolizable energy, the amount of the latter 
required for maintenance will also be proportional to the surface of 
the body. Referring once more to the diagram on p. 410, if OA is 
proportional to the body surface, then OS, which for a given food 
bears a fixed ratio to OA, must also be proportional to the surface. 
If the critical point, K, lies above the maintenance requirement,, 
then the metabolizable energy required for maintenance will equal 
the fasting metabolism, and this, as shown on pp. 359-363, is pro- 
portional to the surface. 

Apparently, then, we are justified in concluding that the mainte- 
nance requirements of different normal animals of the same species 
are proportional to their body surface, or, for approximate computa- 
tions, to the two-thirds power of their live weights. It must not be 
overlooked, however, that the results upon which this conclusion is 
based were obtained largely with the dog, an animal which when at 
rest lies clown, and which, therefore, in these experiments was in a 
state of almost complete muscular relaxation. Our common farm 
animals, on the contrary, pass a considerable portion of their time 
standing, which involves an expenditure of energy in muscular 
work. This expenditure we should naturally assume to be pro- 
portional to the mass to be sustained rather than to its surface, 
and if this be true we have here a second determining factor in the 
maintenance requirement. How important this factor is it is diffi- 
cult to say, although the writer's results with a steer (p. 343) in- 
dicate that it is a large one. Its tendency would be to make the 
maintenance requirement increase more rapidly than the surface. 



NET AVAILABLE ENERGY— MAINTENANCE. 44 1 

Moreover, so far as we can judge from the accounts of Rubner's 
experiments, it would seem likely that what were designated on 
p. 342 as incidental muscular movements are a more important 
factor in determining the maintenance requirements of farm ani- 
mals than they are in fixing that of the dog. 

While, therefore, we are probably justified in retaining pro- 
visionally the computation of the maintenance requirement in 
proportion to the real or estimated surface, it should be with a clear 
understanding that it is at present a deduction from experiments 
on other species and under more or less different conditions. 

Effect of Fattening on Maintenance Requirement. — An interesting 
question, and one of practical importance, is what effect the pro- 
gressive change in weight of the same animal as it is fattened has 
upon its maintenance requirement. We can hardly suppose that 
the internal work of the body will be materially increased by such a 
gain. The increased mass of tissue must involve, of course, some 
increase in metabolism, but all that we know of metabolism of adi- 
pose tissue indicates that it is very sluggish. The most important 
effect might be anticipated to be an increase in the muscular ex- 
ertion required in standing, perhaps counterbalanced to a greater or 
less extent by the tendency of the fat animal to pass more of its 
time in a recumbent position. 

Zuntz & Hagemann * have investigated the effect of a load 
carried on the back upon the metabolism of the horse, and have 
found the latter to be proportional to the total mass (horse plus 
load), but the applicability of this result to another species of ani- 
mal and to an increase of weight caused by fattening may perhaps 
be questioned. The only experiments upon cattle bearing on this 
point are those of Kellner,f who has compared the maintenance 
requirements of fattened and unfattened cattle. It being impossible 
to hit upon exactly the maintenance ration, it is computed from the 
actual results. In case there was a loss of tissue the maintenance 
requirement of the animal is computed by subtracting the poten- 
tial energy of the excreta from the potential energy of food plus 
tissue lost; in other words, the replacement of energy claimed by 
Rubner is assumed to occur. When there was a gain of tissue, on 

* Landw. Jahrb., 27, Supp. Ill, 269. 
fLandw. Vers. Stat., 50, 245; 53, 14. 



442 



PRINCIPLES OF ANIMAL NUTRITION. 



the other hand, the amount of metabolizable energy required to 
produce it is computed on the basis of the results upon utilization 
obtained in other experiments, this larger amount being added to 
the energy of the excreta and the sum of the two subtracted from 
the potential energy of the food; that is the energy of digestion 
and assimilation above the maintenance ration is assumed to be 
waste energy. 

Computed in this way, and assuming further that the mainte- 
nance requirements of different animals are substantially propor- 
tional to the two-thirds powers of their live weights, the results are 
as follows: 



No. of 
Animals. 



Live 

Weight, 

Kgs. 



Stable 
Tem- 
perature, 
Deg. C. 



Main- 
tenance 
Require- 
ment , 
Cals. 



Observed : 

Unfattened 

Fattened 

Computed to same live weight 

Unfattened 

Fattened 



632 

785 



800 
800 



15.2 
15.7 



15.2 
15.7 



13,470 
19,671 



15,760 
19,920 



Kellner concludes from these figures that the maintenance re- 
quirements of fattened animals are greater per unit of surface than 
those of unfattened ones. 

These experiments, it is true, were on different animals and the 
individuality of the animal is an important factor in determining 
the maintenance requirement. The results on the seven unfattened 
animals, when computed to 600 kgs. live weight, show a range of 
1760 Cals., or 13.54 per cent, of the average, while the three results 
on fattened animals, computed to 800 kgs. live weight, show a 
range of 2420 Cals., or 12.16 per cent, of the average. Moreover, 
in making up the average of the unfattened animals, one animal 
was excluded on the ground that the results were probably abnor- 
mally high, but the same animal is subsequently included among 
the three fattened animals the results on which are averaged. 

Even after making all allowances for these facts, however, the 
results for the fattened animals are decidedly higher relatively 



NET AVAILABLE ENERGY-MAINTENANCE. 



443 



than for the unfattened, but how much higher can hardly be deter- 
mined from such averages. 

Comparing the results on the one animal common to the two 
series of experiments we have — 





Live Weight, 
Kgs. 


Maintenance, 
Cals. 


Observed: 

Unfattened 


611.5 
750 

800 
800 


16,835.6 
18,959.6 

20,140 
19,800 


Fattened 


Computed to 800 kgs.: 

Unfattened 


Fattened 





According to the above figures the maintenance ration of this 
animal was practically proportional to the two-thirds power of its 
live weight. On the other hand, however, its maintenance require- 
ment in the unfattened state was much higher than the average 
for the seven unfattened animals, while after fattening it did not 
differ materially from the average for the three fattened animals. 
If, then, we are to regard the above result as correct we must 
assume that by chance all three of the fattened animals had a 
higher normal rate of metabolism than the seven unfattened ones, 
which is not exactly probable. Although this leaves the question 
in a rather unsatisfactory state, it would seem that we must be 
content to let it rest there pending further comparative experi- 
ments on identical animals in different stages of fattening. 



CHAPTER XIII. 
THE UTILIZATION OF ENERGY. 

According to the conceptions discussed in the preceding chap- 
ter a certain portion of the metabolizable energy of the food is 
consumed in what has been called in a broad sense the work of 
digestion and assimilation, while the remainder constitutes net 
available energy and contributes to the maintenance of the store of 
potential energy in the body. If the food is sufficient to supply 
net available energy equal to that dispensed by the internal work 
of the body, the balance between income and expenditure of energy 
is just maintained. If we increase the food beyond this maintenance 
requirement we supply the body with an excess of net available 
energy. In general terms we can say that this excess may be 
disposed of in two ways: it may be utilized for the peformance of 
external work, or it may give rise to a storage of potential energy 
in the body in the form of new tissue,* particularly of fat tissue. 
It appears probable, however, that neither of these processes takes 
place without more or less loss of energy in the form of heat. 
This is certainly true of the performance of muscular work, as has 
already been mentioned (p. 189) and as will be shown in detail 
on subsequent pages. Out of the total potential energy of the 
material metabolized rather more than one third, in the most favor- 
able case, is actually recovered in the form of external work, the 
remainder taking the form of heat. In this case, then, we might 
speak of the coefficient of utilization of the energy as being about 
one third. 

In the utilization of surplus energy by storage of tissue it 
appears likely that there must be also a loss of energy, although, 

* From this point of view the production of milk is to be regarded as 
the formation of new tissue. 

444 



THE UTILIZATION OF ENERGY. 445 

as will appear later, we are not yet in a position to make any such 
definite statements regarding its amount as in the case of muscular 
work, and although the writer's few results on timothy hay cited 
on p. 424 afford no indication of such a loss, the utilization of the 
metabolizable energy for the production of gain seeming to have 
been practically equal to its net availability. It is obvious, how- 
ever, that the conversion of the resorbed nutrients of the food into 
the ingredients of tissue involves profound chemical changes, and 
we can hardly suppose that these take place without some evolution 
of heat. As a good illustration we may take the case of a carbo- 
hydrate. As resorbed into the blood it appears to be in the form 
of a sugar, and it would seem that this sugar can serve, without any 
very extensive chemical changes, to sustain the metabolism incident 
to the internal work of the body; that is, that it is oxidized more 
or less directly in the various tissues to supply energy for their 
physiological work. When, however, a surplus of a carbohydrate 
is to be utilized for the storage of energy in the form of fat, the case 
is different. The formation of fat from a carbohydrate is chemi- 
cally a process of reduction, and the oxygen which is removed 
from the carbohydrate must unite with the carbon and hydrogen 
either of other molecules of the carbohydrate or of other in- 
gredients of food or tissue, in either case giving rise to an evolu- 
tion of heat. If we suppose the transformation to take place 
according to the equation given in Chapter II (p. 24), the re- 
sulting fat would contain about 87 per cent, of the energy of 
the dextrose. Whether this percentage expresses the actual facts 
of the case or not, it is very improbable that this or any similar 
synthetic process takes place in the body without the evolution 
of some heat. 

Provisionally, then, we seem justified in assuming that only a 
part of the net available energy supplied to the organism above 
the maintenance requirement can be utilized to increase the store 
of potential energy in the body, and we may speak in this case, as 
in that of muscular work, of the coefficient of utilization. Repro- 
ducing here the essential parts of the graphic representation 
on p. 410, we may now complete it so as to represent in a general 
and qualitative way the relations indicated above, assuming pro- 
visionally that the effects are linear functions of the food. As 



446 



PRINCIPLES OF ANIMAL NUTRITION. 



before, OG represents the fasting metabolism at a temperature 
below the critical point and OM the critical amount of food at this 
temperature. Then the line GKS represents the availability of 
the food, HLS' the heat production, and OS the maintenance 
requirement. Beyond the point S we may assume that the net 
availability of the food remains the same, represented by the line 
ST. But a fraction of this net available energy, however, can be 




recovered as mechanical work, and its utilization will therefore be 
represented by some such line as $7, while the heat production will 
be correspondingly increased as represented by S'V. Similarly 
the proportion of the net available energy which in the quiescent 
animal is stored up in the form of new tissue may be expressed by 
a line SU and the corresponding heat production by S'U'. What 
the relation between the proportions utilized in the two cases is we 
do not know, and the diagram is intended to be simply schematic; 



THE UTILIZATION OF ENERGY. 447 

but we do know that the proportion is materially greater in the 
latter case, since the heat production of a fattening animal is ob- 
viously much less than that of a working animal utilizing the same 
amount of food. 

In the following pages the attempt has been made to bring 
together the more important experimental evidence bearing upon 
the utilization of food energy for the production of tissue and of 
work. Before, however, proceeding to a consideration of our present 
knowledge upon the subject, attention should be called once more 
to the fact that we are here dealing with it from the statistical point 
of view of the balance between income and expenditure of energy 
of the body. 

In an animal performing work, each muscular contraction 
metabolizes a certain quantity of energy, part of which finally 
appears as heat and part as mechanical work. Besides this, how- 
ever, a secondary result is an increase in the activity of the organs 
of circulation and respiration which requires the expenditure of a 
certain amount of energy, this energy ultimately taking the form 
of heat and being added to that resulting directly from the activity 
of the skeletal muscles. When we compare the actual external 
work done with the total energy metabolized for its performance, 
and so compute the coefficient of utilization, we group all these 
sources of heat production and regard them as, from the economic 
standpoint, a waste of energy, just as in a heat engine the energy 
which escapes conversion into work is regarded as waste energy not- 
withstanding the fact that the loss is inevitable. So, too, in the pro- 
duction of new tissue we look upon total gain of potential energy 
by the body as constituting the net useful result of the feeding, 
and the coefficient of utilization in this case, as in that of muscular 
work, would express the relation which this bears to the net avail- 
able energy supplied in the food. That the effect of abundant 
food may be in some cases to stimulate the metabolism of tissue or 
the " incidental " muscular work (p. 342) is rendered probable by 
Zuntz & Hagemann's results with the horse (see p. 376). All these 
effects are part of the necessary expenditure of energy by the body, 
and however interesting physiologically are statistically sources of 
loss. 



448 PRINCIPLES OF ANIMAL NUTRITION. 

§ i. Utilization for Tissue Building. 

Under this head we have to consider almost exclusively ex- 
periments upon the fattening of mature animals. While the growth 
of young animals and the production of milk are both forms of 
tissue building, the experimental data available seem too scanty 
to justify including them in the scope of the present work. For 
convenience we may first bring together the recorded results and 
later discuss them in their more general bearings. 

One difficulty, however, is encountered at the outset in our 
inadequate knowledge of the net availability of nutrients and 
feeding-stuffs, as pointed out in the foregoing chapter. Until this 
gap is filled it is of course impossible to compare the gain of energy 
by the body with the supply of net available energy. Accordingly 
the results of the experiments upon productive feeding can at present 
be utilized only to determine what proportion of the metabolizable 
energy of the food is recovered in the gain of tissue, and the experi- 
ments cited in the following paragraphs will be considered from 
this point of view. 

Experimental Results, 

Experiments on Carnivora.— In connection with the dis- 
cussion of net availability in the preceding chapter a number of 
experiments were cited (p. 428) in which more or less gain was 
made by the animals. In addition to these Rubner * has made a 
preliminary report of investigations upon the effect of abundant 
feeding on the heat production A dog weighing 25 kgs received 
successively isodynamic amounts of lean meat, fat, and carbo- 
hydrates (kind not stated) equivalent to 155 per cent, of its fasting 
metabolism, a two-days' fast intervening in each case between the 
different rations. Few details are given, but presumably the 
methods were those of Rubner's other experiments already de- 
scribed (compare p. 253). In a second experiment the effects of 
two different amounts of meat were also compared In the follow- 
ing table the results of these experiments have been put into the 
same form as those on net availability in the preceding chapter, the 
data given being per day and head : 

* Sitzungsber. k. bayer. Akad. der Wiss., Math -phys. Classe, 15, 452 



THE UTILIZATION OF ENERGY. 



449 





Metabolizable 

Energy of 

Food, 

Cals. 


Total Gain. 
Cals. 


Gain Over Fasting 
Metabolism. 




Total, 
Cals. 


Per Cent, of 

Energy of 

Food. 


Nothing 

Fat 

Carbohydrates 

Meat -j 



1549 
1549 
1549 
1463 
2181 


-944 
+ 540 

+ 509 
+ 418 
+ 332 
+ 805 


1484 
1453 
1362 
1276 
1749 


95.8 

93.8 
87.9 

87.2 
80.2 



Experiments by Gruber * upon the formation of fat from pro- 
teids (see p. 112) afforded the following results, computed f by 
the use of the factors given on p. 414 : 





Metabolizable 

Energy of 

Food 

Cals. 


Total Gain 
Cals. 


Gain Over Fasting 
Metabolism. 




Total 
Cals. 


Per Cent, of 

Energy of 

Food. 


Nothing 

1500 grms meat: 

1st series 

2d series 

Average 




1325 
1325 

1325 


-743 

250 

296 

273 


993 
1039 

1016 


74.9 

78.4 

76.7 



The difficulty in interpreting these results, as well as those tabu- 
lated on p. 428, as already stated, lies in our imperfect data regard- 
ing the net availability of the materials below the point of mainte - 
nance. Rubner, in discussing his results, assumes an availability 
of 100 per cent., or in other words that the fasting metabolism is 
the measure of the amount of metabolizable energy required for 
maintenance. He accordingly subtracts this amount from the 
total metabolizable energy of the food and regards the remainder 
as excess food, which may be utilized for the storage of energy. 
The percentage utilization of this excess was as shown in the follow- 
ing table, to which Gruber's results, computed by the writer in the 
same way, have been added: 

* Zeit f Biol , 42, 409. 

t From the last two complete days of each series 



45° 



PRINCIPLES OF ANIMAL NUTRITION. 





Mainte- 






Metab • 


nance Re- 






ohzable 


quirement 


Excess 


Cain 


Energy of 


( Fasting 


Food 


Oals 


Food 


Metab- 


Cals. 




Cais. 


olism), 
Cals. 






1549 


944 


605 


540 


1549 


944 


605 


509 


1549 


944 


605 


418 


1463 


944 


519 


332 


2181 


944 


1237 


805 


1325 


743 


582 


250 


1325 


743 


582 


296 



Percent 

age 

Utiliza 

tion. 



Fat 

Carbohydrates 

Meat: 

Rubner 

Gruber \ 



89.3 
84.1 

69.1 
63.9 
65.1 
43.0 
50.9 



As was shown in the preceding chapter, however, while the 
recorded determinations of net availability are far from satisfactory 
they show with a considerable degree of probability that there is 
some loss of energy below the maintenance point and that 100 per 
cent, of net availability is at least not ordinarily reached. A lower 
net availabilty, however, means a larger maintenance requirement, 
and this in turn results in a larger computed percentage utilization 
of the excess food. 

In the following table the latter percentage has been computed 
by the writer for most of the experiments tabulated on p. 428, as 
well as for those of Rubner and Gruber just cited, on the assump- 
tion that the net availability below the maintenance requirement 
was: 

Meat 85 per cent. 

Fat 98 " " 

Starch 90 " " 

Cane sugar 96 " 

The factor for meat is the average of all the results on p. 427; 
that for fat is based on Magnus-Levy's results upon digestive work; 
those for starch and cane-sugar are the averages of Rubner's re- 
sults, omitting those which exceed 100 per cent. By dividing the 
fasting metabolism by the above percentages we may compute the 
amount of mefabolizable energy required for maintenance on the 
above assumption, while subtracting this from the metabolizable 
energy of the food leaves the amount of excess food, which can be 
compared with the observed gain. 



THE UTILIZATION OF ENERGY. 



45 1 



Fasting 
Metab- 
olism. 
Cals. 



Metab- 

olizable 

Energy 

of 


Com- 
puted 
Main- 
tenance, 


Excess 
Food, 
Cals. 


Gain, 
Cals. 


Food, 


Cals. 






Cals, 








1325 


1225 


100 


38 


347 


307 


40 


13 


1549 


1169 


380 


418 


1463 


1169 


294 


332 


2181 


1169 


1012 


805 


1325 


920 


405 


250 


1325 


920 


405 


296 


3298 


1108 


2190 


878 


942 


565 


377 


329 


1884 


565 


1319 


837 


1738 


671 


1067 


1016 


942 


476 


466 


428 


348 


266 


82 


49 


1549 


963 


586 


540 


2015 


1220 


795 


353 


3076 


1220 


1856 


853 


874 


616 


258 


137 


1549 


1049 


500 


509 


572 


470 


102 


190 


702 


325 


377 


365 



Per- 
centage 
Utiliza- 
tion. 



Proteids (meat): 

Pettenkofer & Voit 

Rubner i 

Gruber \ 

Fat: 

Pettenhofer & Voit -I 

Rubner < 

Starch : 

Pettenkofer & Voit -j 

Rubner ("carbohydrates", as- 
sumed to be starch) 

Cane-sugar : 

Rubner 

Cane-sugar and Starch (93 per 
cent, availability) : 
Rubner 



1041 
261 
944 
944 
944 
743 
743 



1086 
554* 
554* 
658 
466 
261 
944 



1098 
1098 
554* 

944 



451 



302 



38.0 
32.5 
110.0 
112.9 
79.6 
61.7 
73.1 



40.1 
87.3 
63.5 
95.2 
91.8 
59.8 
92.1 



44.4 
46.0 
53.1 

101.8 
186.3 

96.8 



While as a whole the results of the computation would seem to 
indicate that the percentage utilization for tissue building is less 
than the percentage availability, the remarkable range of the 
figures and the uncertain basis upon which they are computed do 
not encourage any attempt at a critical discussion. 

Experiments on Man. — The only respiration experiments upon 
man which the writer has been able to find in which any large 
amount of excess food was given are those of Johansson, Lander- 
gren, Sonden & Tigerstedt f already cited on p. 383 in their bearing 
on the subject of digestive work. If we assume, on the basis of 

* Loss on basal ration. 

f Skand. Arch. f. Physiol., 7, 29. 



452 PRINCIPLES OF ANIMAL NUTRITION. 

Magnus-Levy's results, that the work of digestion in man equals 
about 9 per cent, of the metabolizable energy of the food, the 
average results of the experiments are as follows: 

Fasting metabolism 2022 . 4 Cals. 

Metabolizable energy of food 4193 . 4 " 

Computed maintenance requirement 2222.5 " 

Excess food 1970.9 " 

Gain 1676.0 " 

Percentage utilization 85 . per cent. 

The computation gives a somewhat lower percentage for the 
utilization of the excess food than that assumed for the availability 
of the maintenance food. 

Experiments on Swine.— Meissl, Strohmer & Lorenz * in their 
investigation upon the sources of animal fat made six respiration 
experiments with swine, the results of which afford some data as to 
the utilization of their food by these animals. In Experiments V 
and VI, made on two different animals, no food was given, and the 
following results were obtained, the energy equivalent to the loss 
of tissue being computed as in Rubner's experiments in the pre- 
vious chapter: 



Experi- 
ment. 


Tempera- 
ture. 
Deg. C. 


Hours 

Since 

Last 

Feeding. 


Live 

Weight, 

Kgs. 


Loss of 

Nitrogen. 

Grms. 


Loss of 
Carbon, 
Grms. 


Total 
Metab- 
olism, 
Cals. 


Metab- 
olism per 
100 Kgs. 

Live 

Weight,! 

Cals. 


V 

VI.... | 


20 
20 
20.4 


24 
12 

72 


140 
120 
120 


9.80 
9.55 
6.77 


224.51 

375.78 
194.93 


2607 
2291 


2083 
2029 



The experiment begun only twelve hours after the last feeding 
obviously gave too high results, owing to the presence of food in 
the digestive canal. That this source of error was substantially 
eliminated after twenty -four hours appears probable from the close 
agreement of the results with those obtained after seventy-two 
hours. The average fasting metabolism per 100 kgs. live weight 
is 2056 Cals. and this average has been made the basis of the com- 
putations which follow, except in Experiment I. This experiment 

* Zeit. f. Biol., 22, 63. 

t Assumed to be proportional to the two-thirds power of the weight. 



THE UTILIZATION OF ENERGY. 453 

having been made on the same individual as Experiment V, the 
result of the latter is used directly. 

In Experiments I and II the ration consisted of rice, in Experi- 
ment III of barley, and in Experiment IV of rice, flesh-meal, and 
whey. In all cases large amounts of food were consumed and a 
rapid production of fat was observed. The digestibility of the food 
was determined. Its metabolizable energy has been computed by 
the writer from the results of the digestion experiments by the use 
of the following factors:* 

1 gram digestible protein 4.1 Cals. 

1 " nitrogen-free extract. . . 4.2 " 

1 " " crude fiber 3.5 " 

1 " " ether extract 8.8 " 

No attempt was made in these experiments to determine the 
methane, if any existed, in the respiratory products. The results 
per day and head were as follows: 



Experiment. 


Tem- 
perature, 
Deg. C. 


Live 

Weight, 

Kgs. 


Computed Metab- 
Fasting | olizable 
Metabolism,, Energy. 
Cals. Cals. 


Energy of 
Gain, Cals. 


Nutritive 
Ratio. 


I 

II 

Ill 

IV 


18.0 
18.5 
19.3 
16.7 


140 

70 

125 

104 


2607 7157 
1621 7167 
2386 5125 f 
2111 6129 


3464 
4048 
1774 
2556 


1 :15.4 
1 : 14.1 
1 : 9.3 

1 : 2.4 



No determinations were made of the actual requirements for 
maintenance as distinguished from the fasting metabolism, and 
hence the data are lacking for a computation of the net availability 
of the metabolizable energy of the food on the one hand and the 
percentage utilization of the excess food on the other. Cooke's re- 
sults mentioned on p. 438, however, seem to give some indication 
that the maintenance demand of swine may not be greatly in excess 
of the fasting metabolism. If in these experiments we assume the 
same net availability as that just assumed in the case of man, viz., 
91 per cent., we obtain the following figures: 

* Compare p. 332. 

f In this experiment the ether extract of the feces exceeded that of the 
food by 23.95 grms. This excess has been assumed to have a heat value 
of 4.2 Cals. per grm. and a corresponding amount deducted from the com- 
puted energy of the other digested nutrients 



454 



PRINCIPLES OF ANIMAL NUTRITION. 



s 

a 

<u 

ft 

H 

W 


Food. 


Nutri- 
tive 
Ratio. 
1- 


Com- 
puted 
Fasting 
Metab- 
olism, 
Cals. 


Metab- 
olizable 
Energy 

of 
Food, 
Cals. 


Com- 
puted 
Main- 
tenance 

Re- 
quire- 
ment, 
Cals. 


Excess 
Food, 
Cals. 


Gain, 
Cals. 


Per- 
cent- 
age 
Utiliza- 
tion. 


T 




15.4 

14.1 

9.3 

2.4 


2607 
1621 
2386 

2111 


7157 
7167 
5125 

6129 


2865 
1781 
2622 

2320 


4292 
5386 
2503 

3809 


3464 
4048 
1774 

2556 


80.7 


TT 


it 


75.2 


TTT 


Barley 


70.9 


IV 


Rice, flesh-meal, 


67.1 



It is interesting to note that the utilization as thus computed 
diminishes as the proportion of protein in the ration increases, a 
result which the low average figures obtained on pp. 427 and 450 
for the availability and the percentage utilization of the proteids 
would lead us to expect. Obviously, however, too much value 
should not be attached to such computations as the above. 

Kornauth & Arche * in an investigation on the feeding value of 
cockle have also made respiration experiments with a swine. The 
food consisted in Period II of cockle, barley, and maize, and in< 
Period III of rape-cake, barley, and maize, the amounts of the 
several nutrients actually digested being nearly the same in the 
two periods. In each period two respiration experiments were 
made which gave concordant results. The following table contains 
the average results for each period computed on the same basis as in 
the experiments of Meissl, Strohmer & Lorenz. No fasting experi- 
ments having been made, the average results of the experiments by 
the last-named authors have been used, the average live weight of 
50 kgs. being taken as the basis. 



"3 

0) 

» 

a 

M 


Food. 


Nutri- 
tive 
Ratio. 
1: 


Esti- 
mated 
Fasting 
Metab- 
olism. 
Cals. 


Metab- 
olizable 
Energy 

of 
Food, 
Cals. 


Com- 
puted 
Main- 
tenance 

Re- 
quire- 
ment, 
Cals. 


Excess 
Food, 
Cals. 


Gain, 
Cals. 


Per- 
centage 
Utiliza- 
tion. 


II 


Cockle, barley, and 
maize 


6.7 
6.2 


1296 
1296 


.3057 
3101 


1424 
1424 


1633 
1677 


1170 
1095 


71.7 


III 


Rape-cake, barley, 


65.3 



* Landw. Vers. Stat., 40, 177. 



THE UTILIZATION OF ENERGY. 455 

The percentages as thus computed are seen to agree fairly well 
with the ones computed for those of Meissl, Strohmer & Lorenz's 
experiments in which the proportion of protein in the food was 
similar. 

Experiments on Ruminants. — Experiments upon ruminants 
necessarily differ in one important respect from those hitherto con- 
sidered. With carnivora and with swine it is possible to determine 
the fasting metabolism, or, in other words, to trace the line repre- 
senting the net availability or the utilization throughout its entire 
extent. With herbivora, and particularly with ruminants, this is 
practically impossible, for obvious reasons, and the course of the 
lower portion of the line is imaginary. This, however, is no obsta- 
cle to a determination of the net availability or percentage utiliza- 
tion of the food within the limits as to amount prescribed by the 
nature of the animals. As is clear from the graphic discussion of 
the problem on pp. 410 and 446, all that is necessary is to determine 
the gain or loss of energy by the body corresponding to two different 
amounts of food above or below maintenance. A simple com- 
parison of differences then gives in the one case the percentage 
utilization and in the other the net availability of the energy of the 
food added. The method is the same principle as that already 
employed in computing the metabolizable energy of the added 
food. 

The Mockern Experiments. — The very extensive and elabo- 
rate investigations upon cattle at the Mockern Experiment Station 
by G. Kiihn and Kellner,* which have already been discussed in 
relation to the metabolizable energy of the food, are also our chief 
source of knowledge regarding the utilization of this energy by 
ruminants and will necessarily constitute the principal basis of the 
present discussion. 

These experiments were chiefly upon the fattening of mature 
cattle, various additions being made to basal rations which were 
themselves in almost every case more than sufficient for maintenance. 
The actual gain of carbon and nitrogen by the animals, both on the 
basal and the augmented rations, was accurately determined, and 
from the data thus obtained the gain of proteids and fat and of 
energy was computed in the usual way. By a comparison of the 
*Landw. Vers. Stat., 44, 257; 47,275; 50,245; 53,1. 



45 6 PRINCIPLES OF ANIMAL NUTRITION. 

gains on the basal and on the augmented ration, then, we may deter- 
mine what proportion of the metabolizable energy of the added 
food was stored in the gain of tissue. In other words, we may 
determine two points on the line SU in the figure on p. 446, 
thereby determining the line if it is a straight line. 

If the added metabolizable energy of the larger ration were de- 
rived solely from the material added, the result would show the utili- 
zation of the energy of that material. As we have seen, however, in 
connection with the discussion of the metabolizable energy of the food 
in Chapter X, this is rarely if ever the case with herbivorous animals. 
The difference in metabolizable energy between two rations usually 
includes, in addition to the real metabolizable energy of the added 
food, differences in the digestibility of the original ration and in 
the losses in urine and methane. Accordingly, we are here con- 
fronted with the same alternative as before, viz., whether to attempt 
to eliminate these secondary effects and base our computations 
on the real metabolizable energy of the feeding-stuff under experi- 
ment or to take the apparent metabolizable energy as representing 
the actual amount of energy contributed to the metabolism of the 
body. In the one case, if successful, we shall obtain a result which 
will be physiologically correct but which when applied in practice 
will require modification for the secondary effects just mentioned. 
In the other case we shall have a summary expression including 
all these results, but with the disadvantage of being more or less 
empirical in its nature. Either method has its advantages and 
disadvantages. In the present case we shall use the apparent 
metabolizable energy of feeding-stuffs as computed on pp. 285-297 
and in Tables I- VI of the Appendix as the basis of computation. 
This does not, of course, affect the absolute amount of energy 
utilized from a unit weight of the material, but only the percentage 
calculated upon the metabolizable energy. 

Sources of Uncertainty in Computation. — While the computation 
of the energy utilized from feeding-stuffs in the manner just indi- 
cated is in principle very simple, certain complications arise in its 
execution from the impossibility of securing exactly comparable 
conditions of experiment. Two of these in particular require 
consideration here. 

Differences in Organic Matter Consumed. — As was noted in the 



THE UTILIZATION OF ENERGY. 457 

discussion of the metabolizable energy of feeding-stuffs, the un- 
avoidable slight variations in the moisture-content of the latter 
in the Mockern experiments resulted in slight differences in the 
amounts of organic matter of the basal ration consumed in the 
several periods. A comparison, then, between two periods, as re- 
gards metabolizable energy and resulting gain, shows the effect of 
the added feeding-stuff plus the effect of this small difference. 
For the metabolizable energy an approximate correction was com- 
puted. In order to make a similar correction in the resulting gain 
of tissue, however, it is necessary to know to what extent this 
difference in metabolizable energy contributed to the observed 
gain; that is, to know the percentage utilization of the basal ration. 
No direct determinations of this factor, however — that is, no com- 
parisons of the results of feeding different amounts of the basal 
ration — were made. In his discussion of the results Kellner virtually 
assumes a percentage of utilization by subtracting from the total 
metabolizable energy of the food the average amount required for 
maintenance as determined by his own experiments and then com- 
paring the energy in excess of the maintenance requirement with 
the resulting gain. 

Differences in Live Weight. — The live weights of the animals in 
the Mockern experiments differed considerably in the different 
periods. This would probably result in differences in the require- 
ments for maintenance, although the data at hand seem insufficient 
to satisfactorily determine the relation between live weight and 
maintenance (see p. 441). Kellner assumes that the maintenance 
ration is in proportion to the two-third power of the live weight, a 
result which has already been shown to correspond fairly well with 
the results upon Ox B, although in apparent conflict with the aver- 
age results obtained on other animals. 

Utilization of Basal Ration. — In order to be able to correct the 
results for differences in organic matter consumed and differences 
in live weight, it is necessary, as has just been pointed out, to know 
the percentage utilization of the basal ration. This Kellner assumes 
in assuming a maintenance ration. There are, however, serious ob- 
jections to this method of procedure. First, the maintenance ration 
used by Kellner is an average, based on results which were obtained 
with a number of animals, not including all those used in the fatten- 



458 PRINCIPLES OF ANIMAL NUTRITION. 

ing experiments, and which show a range of 13.5 per cent, of the 
average. Second, the computed maintenance ration is based upon 
experiments with coarse fodder only. We have seen reason to be- 
lieve, however (pp. 388-391) that the net availability of the metabo- 
lizable energy in coarse fodders is decidedly less than in case of con- 
centrated feeds, and that consequently more metabolizable energy 
would be required for maintenance on a ration composed of coarse 
fodder than on one containing concentrated feeds, as did Kellner's 
basal rations. In other words, Kellner's assumed maintenance 
ration is probably somewhat too large and his computed utiliza- 
tion of the basal ration, therefore, also somewhat too high. Third, 
it is by no means demonstrated that the maintenance ration of 
fattened as compared with unfattened animals is, as Kellner as- 
sumes, in proportion to the two-third power of the live weight. 

In the absence of any direct determinations of the utilization 
of the basal rations, however, there seems to be no course open but 
to follow substantially Kellner's method of computation and assume 
a maintenance ration for each of the animals in proportion to the 
two-thirds power of its live weight during the period under con- 
sideration. 

Computation of Results.— -The method of computing the correc- 
tions for the differences in live weight and in the amount of the 
basal ration consumed may be illustrated by the same two periods 
which were used on pages 288-9 to exemplify the computation of 
metabolizable energy, viz., Periods 4 and 7 with Ox H, on meadow 
hay. In Period 4, on the basal ration, the live weight was 668.9 
kgs., the computed maintenance requirement 13,989.1 Cals., and 
the gain by the animal 2003.2 Cals. The percentage utilization 
therefore was as follows : 

Metabolizable energy of ration 17,388.8 Cals. 

Computed maintenance requirement . . 13,989.1 " 

Excess food 3399.7 Cals. 

Gain 2003.2 « 

Percentage utilization 58.9 % 

In Period 7 the total metabolizable energy of the ration was 
26,013.0 Cals. and the gain 5643.2 Cals. Of the excess of 8624.2 



THE UTILIZATION OF ENERGY. 



459 



Cals. over Period 4, however, it was computed that 119.4 Cals. were 
due to an increased consumption of the ingredients of the basal 
ration, leaving 8504.8 Cals. as the metabolizable energy of the 
added hay! This 119.4 Cals., however, contributed to the increased 
gain of 3640.0 Cals. made by the animal. If we assume the per- 
centage 58.9 just computed to apply to it, the corresponding gain 
would be 119.4 X 0.589 or 70.3 Cals., leaving 3569.7 Cals. as the 
gain produced by the 8504.8 Cals. of metabolizable energy derived 
from the meadow hay. 

In Period 7, however, the animal weighed 736.0 kgs., and his 
computed maintenance requirement was therefore 14,909.6 Cals. of 
metabolizable energy, or 920.5 Cals. more than in Period 4. In 
other words, if he had weighed no more in Period 7 than in Period 
4, there would have been 920.5 Cals. more metabolizable energy 
which could have served to produce a gain of tissue. Assuming, as 
before, that 58.9 fo of this would be stored in the body, the result- 
ing gain would have been 920.5 X 0.589 or 542.2 Cals. Adding this 
to the gain of 3569.7 Cals. just computed makes a total of 4111.9 
Cals. as the computed gain to be credited to 8504.8 Cals. of metab- 
olizable energy in the hay added, which is equivalent to a per- 
centage utilization of 48.4 per cent. Expressed in tabular form, 
the results of these comparisons are as follows : — 





3 
Ej 

'3 
< 

H 

11 


— i 

o 

'u 

?M 

7 
4 


Average 

Live Weight, 

Kgs. 


Metabo- 
lizable 
Energy, 
Cals. 


Com- 
puted 
Mainte- 
nance, 
Cals. 


Excess 

over 
Mainte- 
nance, 

Cals. 


Energy 
of Gain 

(Cor- 
rected), 

Cals. 


Percentage 1 
Utilization 
of Excess. 


Meadow Hay, VI: 

Basal ration + hay 

Correction for organic matter 


736.0 
668.9 


26.013.0 
-119.4 


14,909.6 
13,989.1 


11,103.4 
-119.4 


5,643.2 
-70.3 




Correction for live weight . . . 


25,893.6 

17,388.8 
8,504.8 


10,984.0 
+ 920.5 


5.572.9 
+ 542.2 






11,904.5 
3,399.7 


6.115.1 
2.003.2 


58.9 






8,504.8 


4,111.9 


48.4 





Table VII of the Appendix contains the details of the computa- 
tions of percentage utilization according to the above method. 
The results differ somewhat from those reported by Kellner,* 
* hoc. cit., pp. 63, 133, 226, and 334. 



460 PRINCIPLES OF ANIMAL NUTRITION. 

first, because they include a correction for the differences in or- 
ganic matter consumed, and second, because the energy of the gain 
has been corrected for the amount of nitrogen retained in the body 
in the same manner as the energy of the urine (compare p. 285), 
viz., by deducting 7.45 Cals. per gram of nitrogen. In most cases 
the metabolizable energy is that already computed in Tables I to 
VI of the Appendix, being based on actual calorimetric determina- 
tions in food and feces. In two instances (distinguished by being 
bracketed) the metabolizable energy has been computed by the 
writer from such data as are available.* 

In Table VII the final results are expressed as percentages of 
the metabolizable energy utilized. By combining them with the 
results contained in the six preceding tables of the Appendix they 
may likewise be expressed as percentages of the gross energy of 
the several materials and also as energy utilized per gram of total 
organic matter. The summary on pp. 461-2 contains the results 
expressed in all of these ways. 

Earlier Experiments. — The earlier respiration experiments 
of Henneberg & Stohmann f on oxen, in 1865, while made in accord- 
ance with the experience then available, are now known to be de- 
fective in several respects. The respiratory products were deter- 
mined for twelve hours only, while the same authors subsequently 
showed that twenty-four hours was the minimum time necessary. 
The food consumed on the respiration day was less than the average 
for the whole experiment, but how much less does not appear, and 
finally the methods used for the determination of the hydrocarbon 
gases excreted have subsequently been shown to give too low re- 
sults. It seems useless therefore to enter into an elaborate com- 
putation of the results. In the later experiments of the same 
authors % with sheep, these sources of inaccuracy were largely re- 

* The data used in these computations are as follows : 

For Ox IV the average results for Periods la and lfe have been com- 
puted on the assumption that the heat values of food and excreta per gram 
in Period \b were the same as those determined in Period la 

For Ox V the metabolizable energy in Period 3 has been computed by 
adding to that in Period la 3 345 Cals. for each gram of organic matter in 
the starch added, this being the metabolizable energy computed for the 
starch in Period 2a, 

t Neue Beitrage, p. 287. % Loc. cil , p 68. 



THE UTILIZATION OF ENERGY. 



461 



ENERGY UTILIZED. 



Per Cent, of 

Metabo- 

lizable 

Energy. 



Per Cent, of 

Gross 

Energy. 



Per Grm. 

Total 
Organic 
Matter. 



Meadow Hay : 

Sample V, Ox F 

" V, " G 

Average 

Sample VI, Ox H, Period 2. 
" VI, " H, " 7. 
" VI, " J 

Average 

Average V and VI 

Oat Straw : 

Ox F 

" G 

Average 

Wheat Straw : 

Ox H 

" J 

Average 

Extracted Rye Straw : 

OxH 

" J 

Average 

eet Molasses : 

Sample I, Ox F 

" II, " H 

" II, " J 

Average 

Starch — Kilhn's Experiments : 

Sample I. Ox III 

" I, " IV 

Average 

Sample II. Ox V, Period 2a 
" II. " V, " 2b. 

n, " v, " 3 

" II, " VI, " 26 
' : II. " VI, " 3 . 

Average 

Average I and II 



40.4 
36.2 



38.3 

50.4 
48.4 
34.8 



44.5 
41.4 



38.8 
33.4 



36.1 



10.8 
24.0 



17.4 



67.3 
58.6 



63.0 



58.5 
83.4 
50.2 



66.8 



50.0 
49.2 



49.6 

53.2 
53.7 
59.7 
48.1 
46.6 



50.4 
50.0 



16.5 
15.9 



16.2 

26.5 
26.1 
18.5 



23.7 
20.0 



14.2 
11.7 



12.9 



3.2 

7.8 



5.5 



51.6 
43.6 



47.6 



41.6 
65.9 
36.5 



51.2 



35.6 
31.3 



33.5 

42.0 
40.1 

34.3 
32.6 



37.3 
35.4 



0.780 
0.756 



0.768 

1.266 
1.247 

0.883 



1.132 
0.950 



0.682 
0.564 



0.623 



0.153 
0.373 



0.263 



2.194 
1.854 



2.024 



1.700 
2.760 
1.529 



2.145 



1.514 
1.331 



1.423 

1.779 
1.699 

1.452 
1.380 



1.578 
1.501 



462 



PRINCIPLES OF ANIMAL NUTRITION. 



ENERGY UTILIZED {Continued). 



Starch — Kellner's Experiments : 

Sample I and II, Ox B 

" I " II, " C 

Average 

Sample III, Ox D 

Ill, " F 

III, " G 

Average 

Sample IV, Ox H 

IV, " J 

Average 

Average III and IV 

Wheat Gluten — Kiihn's Experiments : 

Ox III, Period 3 

" III, " 4 

Average. 

Ox IV 

Wheat Gluten — Kellner's Experiments 

Sample I, Ox B, Period 1 

I, " B, " 3 , 

" I, " C 

Average , 

Sample II, Ox D 

Average of I and II 

Peanut Oil . 

Sample I, Ox D , 

" II, " F 

" II, " G 

Average 



Per Cent, of 
Metabo- 
lizable 
Energy. 



65.4 
57.6 



61.5 

53.7 

64.8 
65.8 



61.4 

56.0 

54.8 



55.4 

58.4 



45.3 

48.0 



46.7 
58.2 



36.9 
49.7 
43.2 



43.3 
37.3 

40.3 



51.6 
65.1 
69.4 



67.3 



Per Cent, of 

Gross 

Energy. 



31.8 
28.0 



29.9 

36.1 

46.2 
50.9 



44.4 

44.4 
39.5 



42.0 
43.2 



37.0 
35.8 



36.4 
58.9 



19.6 
32.6 
30.9 



27.7 
26.1 
26.9 



40.1 
34.2 
41.2 



37.7 



Per Grm 

Total 
Organic 
Matter 



1.325 
1.168 



1.247 

1.500 
1.922 
2.116 



1.846 

1.855 
1.652 



1.754 
1.800 



2.289 
2.213 



2.251 
3.645 



1.115 

1.849 
1.850 



1.605 
1.516 
1.561 



3.811 
3.238 
3.903 



3.571 



THE UTILIZATION OF ENERGY. 463 

moved, but the experiments were upon maintenance feeding only 
and afford no data for a computation of utilization. 

A series of respiration experiments on sheep was made by 
Kern & Wattenberg at the Gottingen-Weende Experiment Station 
in 1879, the results of which were reported after Kern's death by 
Henneberg & Pfeiffer.* Varying quantities of nearly pure proteids 
(conglutin or flesh-meal) were added to a basal ration of hay and 
barley meal, the amount of proteids in the ration being regularly 
increased by about 50 grams in each of four successive periods and 
then similarly diminished through three more periods. 

The experiments suffered from some defects in technique which 
later experience has remedied, the results most strikingly affected 
being those for the amount of methane excreted. For the first 
two periods no results are reported; for the remaining periods they 
are quite variable, and those on different days of the same period 
differ widely. The authors consider that their figures represent 
the minimum amount present, and in their final computations use 
the average of all the five periods as the basis for estimating the 
quantity of carbon excreted in this form. The amounts as actually 
determined showed a considerable diminution in the periods in 
which most proteids were fed, contrary to Kiihn's results, but it is 
worthy of note that the average proportion of carbon dioxide to 
methane was not much different from that found by the latter. 
The determinations of carbon dioxide in the respiratory products 
likewise showed considerable fluctuations from day to day, but as 
the results are mostly the average of three or four trials of twenty- 
four hours each it may be assumed that these variations are more 
or less compensated for. The respiratory products were determined 
for both animals together, although ail the other data were secured 
for each individual. The results given on the following pages, 
therefore, are the totals for both animals. 

It is stated that addition of proteids to the ration resulted in 
the diminution, and final disappearance in the middle period, of the 
hippuric acid of the urine, but the actual amounts present are re- 
ported only for the first and last periods. It is not possible, there- 
fore, to make any satisfactory computation of the energy of the 
urine or of the proper factor for the metabolizable energy of the 
digested proteids of the total ration. By another method of com- 
* Jour. f. Landw., 38. 215. 



464 



PRINCIPLES OF ANIMAL NUTRITION. 



putation, however, it seems possible to secure an approximate idea 
of the relation of added food to gain. 

By subtracting from the food digested in Periods II-VI the 
average amount digested in Periods I and VII, on the basal 
ration, we find the amounts of added food, consisting chiefly of 
proteids. Reckoning the metabolizable energy of the added pro- 
teids at 4.958 Cals. per gram (compare p. 317), that of the crude 
fiber and nitrogen-free extract at 3.674 Cals., and that of the ether 
extract at 8.322 Cals., we get the approximate metabolizable energy 
of the added food, and can compare it with the energy of the corre- 
sponding gain. Thus for Period II we have the following: 



DIGESTED. 





Protein,* 
Grms. 


Crude 
Fiber, 
Grms. 


Nitrogen- 
free 
Extract, 
Grms. 


Ether 

Extract 

Grms. 


Period II 


211.33 

101.05 


280.77 
277.91 


643.22 
633 . 12 


20.88 


Periods I and \ II 


21.60 






Difference 


110.28 

Cals. 
546.8 


2.86 


10.10 


-0.72 




, 




Equivalent metabolizable 


12 
Cals. 
47.6 


.96 


Cals. 
-6 









* Protein of basal ration and of feces equals N X 6 . 25 ; that of 
or flesh-meal equals its total organic matter. 



dutin 



GAIN. 





Protein Grms. 


Fat, Grms. 


Period 11 


15.00 
6.85 


69.27 
19.66 


Periods I and VII. . . 

Difference 

Equivalent energy 


8.15 
Cals. 
46.3 


49.61 
Cals. 
471.5 



The figures for the gain are those given by the authors, based 
on the assumption of a uniform excretion of methane throughout 
the experiments; the gain of protein includes that contained in the 
wool produced. The animals gained slightly in weight, in addition 
to the growth of wool. Computed on this basis, the percentage of 
the energy of the added food which was utilized was as follows: 



THE UTILIZATION OF ENERGY. 



465 



Period. 


Metabolizable 

Energy of 

Added Food, 

Cals. 


Energy of 

Resulting Gain. 

Cals. 


Per Cent. 
Utilized. 


( II 


588.4 
1100.3 
1639.2 
1131.7 

454.9 


517.8 
741.8 
1106.8 
672.5 
315.7 


88.00 


Conglutin: < III 


67.42 


( iv 

„, , , | V 


67.51 
59.41 


Mesh- meal: < yj 


69.39 







A computation based on the observed amounts of methane 
would affect the above figures in two ways. First, if the added 
proteids diminished the production of methane, this was equivalent 
to an increase in the apparent metabolizable energy of the food, 
and the figures for the latter must be correspondingly increased. 
Second, the gain of fat will also appear relatively greater in the 
intermediate periods, II- YT, and the figures for the energy of the 
gain must also be increased. Computed on this basis the results 
are: 



Period. 


Energy of 

Added Food, 

Cals. 


Energy of 

Resulting Gain, 

Cals. 


Per Cent. 
Utilized. 


( II 

Conglutin: < III 

( IV 


715.4 
1245.8 
1902.3 
1288.2 

582.1 


605.7 
842.4 
1288.8 
780.7 
403.6 


84.68 
67.63 
67.76 


™ , , ( V 


60.59 


I lesh-meal : -j y-r 


69.33 







No obvious explanation of the exceptionally high results ob- 
tained in Period II presents itself. Those of the remaining 
periods do not seem to indicate any considerable differences in the 
utilization of different quantities. The figures are notably higher 
than those computed from the Mockern experiments, but in view 
of the uncertainties attaching to them too much stress should not 
be laid on this fact. 

Discussion of Results. 

As was pointed out at the beginning of this section, and as was 
further apparent in considering the results of experiments upon 
carnivora, our knowledge of the net availability of the energy of 
feeding- stuffs and nutrients is too imperfect to permit the experi- 



466 PRINCIPLES OF ANIMAL NUTRITION. 

mental results above detailed to be discussed from the standpoint 
of the percentage utilization of the net available energy. 

Furthermore, even confining ourselves to a consideration of the 
utilization of the metabolizable energy of the food, we have already 
seen that the recorded results upon carnivorous animals show such 
wide divergencies as to render it difficult if not impossible to draw 
any quantitative conclusions from them. 

For the present, accordingly, our discussion of the utilization 
of energy must be confined chiefly to the results which have been 
reached with herbivora, and in the main to the Mockern experi- 
ments, and we must content ourselves with an attempt to trace the 
relations between metabolizable energy and energy utilized, or, to 
look at the subject from the other point of view, with determining 
the proportion of the metabolizable energy of the food which is 
expended in the combined work of digestion, assimilation, and 
tissue building. From the practical standpoint this is of course 
the important thing, since either form of expenditure of energy 
constitutes, in the economic aspect of the matter, a waste, but it 
is nevertheless to be regretted that it is at present impossible to 
further analyze this waste. 

Influence of Amount of Food. — As in the discussion of net 
availability in Chapter XII, we have thus far assumed the energy 
utilized to be a linear function of the net available or of the metabo- 
lizable energy of the food. Before proceeding further it becomes 
important to consider how far this assumption is justified by the 
facts on record. 

Carnivora. — Of the experiments upon camivora recorded on 
preceding pages, those of Rubner with different amounts of meat, 
when computed by his method (that is, assuming an availability of 
100 per cent, below the maintenance point, as on p. 450). appear to 
indicate that the utilization above that point is constant. If, how- 
ever, a lower percentage of availability is assumed, as on p. 451, 
this constancy disappears. None of the other results there sum- 
marized seem suitable for discussion from this point of view. 

Swine. — If in the experiments of Meissl, Strohmer & Lorenz, as 
computed on p. 454, we express the estimated metabolizable energy 
of the excess food as a percentage of the fasting metabolism, we 
have the following comparison of the percentage utilization with 



THE UTILIZATION OF ENERGY. 



467 



the relative amount of excess food, to which may be added Kor- 
nauth & Arche's results similarly computed: 





Excess Over 

Fasting 

Metabolism, 

Per Cent. 


Percentage 
Utilization. 


Meissl : 

Experiment I ........ . 


133 

250 

74 

180 

126 
129 


80.7 
75.2 
70.9 
67.1 

71.7 
65.3 


II 


Ill 


IV 


Kornauth & Arche : 

Experiment III 


" IV 





While there is some variation in the percentage utilization, as 
would naturally be expected in experiments with different animals, 
the range in the relative amount of excess food is much greater 
and there is no indication of a connection between the two. 

Ruminants. — The earlier Mockern experiments by G. Kiihn 
include one upon wheat gluten and two upon starch in which two 
different quantities were added to the basal ration of the same 
animal. The final results were as follows : 



Animal. 



Period 



Added to 

Basal Ration. 

Kgs 



Percentage 

Utilization 

of Metaboliz- 

able Energy. 



Wheat gluten. 



Starch . 



Ill 

111 

V 

V 

V 

VI 

VI 



3 

4 

2a 

2b 

3 

2b 

3 



0.68 

1.36 

2.0 

2.0 

3.5 

2.0 

3.5 



45.3 
48.0 
53.2 
53.7 
59.7 
48.1 
46.6 



These results do not indicate that any material effect is exerted 
upon the utilization of the metabolizable energy of the food by 
the amount consumed, since the differences are small in themselves 
and in both directions. 

The results, reported by Pfeiffer, of experiments upon the addi- 
tion of varying amounts of proteids to a basal ration, as computed 
by the writer (p. 465), likewise show a fairly constant percentage 



468 



PRINCIPLES OF ANIMAL NUTRITION. 



utilization of the energy of the proteids used, with the exception 
of the strikingly higher result of the first period. 

A similar conclusion may be drawn from a study of the Mockern 
results as a whole, as recorded in Table VII of the Appendix. 
While the computed percentages in each series vary more or less 
in the different experiments, the differences are in most cases not 
large and appear to bear no relation either to the total quantity 
of food given or to the amount of the particular food under experi- 
ment which was added to the basal ration, but to be due rather 
to individual differences in the animals. This is strikingly shown 
in the following table, in which the results upon hay, wheat gluten, 
and starch are arranged in the order of the percentage utilization : 









Metaboliz- 


Total Excess 


Percentage 








able Energy 


Over Com- 


Utilization 


Feeding-stuff. 


Animal. 


Period. 


of Added 


puted Main- 


of Metabo- 








Food, 


tenance, 


lizable 








Cals. 


Cals. 


Energy. 




J 


2 


7875 


12,192 


34.8 




G 


2 


5726 


9,780 


36.2 


Meadow hay < 


F 


1 


5506 


10,184 


40.4 




H 


7 


8505 


11,905 


48.4 




H 


2 


7875 


11.275 


50.4 


r 


B 


1 


4483 


15,129 


36.9 




D 


4 


5713 


17,373 


37.3 




C 


3 


6033 


19,635 


43.2 




III 


3 


2913 


8,982 


45.3 




III 


4 


5332 


11,401 


48.0 




B 


3 


5507 


16,153 


49.7 


I 


IV 


3 


3645 


7,132 


58.2 


' 


VI 


3 


8264 


12,364 


46.6 




VI 


26 


5038 


9,138 


48.1 


Starch — Kilhn'sexpts. . - 


IV 
III 


2 
2 


4350 
4998 


3411 
6,592 


49.2 
50.0 




V 


2a 


5425 


8,821 


53.2 




V 


3 


9658 


13,054 


59.7 


r 


D 


2 


4420 


16,080 


53.7 




J 


3 


4826 


9,142 


54.8 




H 


3 


6668 


10,068 


56.0 


Starch — Kellner's expts \ 


C 


2 


3027 


16,829 


57.6 


\ 


F 


4 


5009 


9,686 


64.8 


1 


B 


2 


3291 


13,937 


65.4 


1 


G 


4 


5387 


9,441 


65.8 



But while this is true of each series by itself, a comparison of 
the two series upon starch leads to a different conclusion. In 
Kuhn's experiments the basal rations consisted largely or exclu- 
sively of coarse fodder. In Kellner's experiments the starch was 



THE UTILIZATION OF ENERGY. 469 

added to a materially heavier basal ration containing considerable 
grain and therefore already tolerably rich in starch and other carbo- 
hydrates. In spite of the smaller average amounts of starch added, 
then, Kellner's results in a sense represent the percentage utiliza- 
tion of larger quantities of starch than do Kiihn's; that is, they 
represent the utilization of starch at a greater distance above the 
maintenance ration. The average utilization (pp. 461-2) was — 

Kiihn's experiments 50.0 per cent. 

Kellner's experiments, moderate rations ... 58.4 " " 
" " heavy rations 61.5 " " 

It would appear, then, from these figures that the metaboliz- 
able energy of starch was more fully utilized in rations containing a 
relatively large quantity of it. At least a partial explanation of 
this seems to be afforded by the variations in the production of 
hydrocarbons (methane). As was mentioned in discussing the 
metabolizable energy of starch, the conditions in Kiihn's experi- 
ments were such as to permit a considerable proportion of the 
starch to undergo the methane fermentation, while the more abun- 
dant supply of it in Kellner's experiments resulted in. reducing, or 
in some cases wholly suppressing, this fermentation of the starch. 
The effect of this, as there pointed out. was to make the metaboliz- 
able energy per gram greater in Kellner's than in Kiihn's experi- 
ments, but it has also another result. As we have seen, the methane 
fermentation constitutes part of the work of digestion, in the general 
sense in which that term is here employed, the amount of the latter 
being measured by the heat evolved. This amount being less in 
Kellner's than in Kiihn's experiments, the net availability of the 
metabolizable energy of the starch should be greater, and, other 
things being equal, the storage of energy (gain of tissue) should also 
be greater. 

Kellner * computes that for each 100 grams of starch digested 
there was produced, on the average, methane corresponding to the 
following amounts of carbon: 

In Kiihn's experiments 3.0 grams 

In Kellner's experiments : 2.3 " 

* Loc tit., p. 423. 



47o PRINCIPLES OF ANIMAL NUTRITION. 

An approximate computation of the probable differences in the 
heat evolved by the fermentation, based on such data as are avail- 
able; gives as a result 0.159 Cal. per gram of starch, or somewhat 
more than one-half the difference in average utilized energy, viz., 
0.265 Cal. per gram. The data on which the computation is based, 
however, are too uncertain to allow us to attach very much value 
to the results, except perhaps as an indication that xhe supposed 
cause of the difference in the utilization of the energy is insuffi- 
cient to fully account for the effect. 

Conclusions. — It cannot be claimed that the above results are 
sufficiently extensive or exact to permit final conclusions to be 
drawn, but their general tendency seems to be in favor of the hy- 
pothesis that the proportion of energy utilized is substantially inde- 
pendent of the quantity of food, provided that the changes in the 
latter are not so great as to modify the course of the fermentations 
in the digestive tract. The results upon starch just considered 
seem to indicate that if the variations in quantity or make-up of 
the ration are pushed beyond that point, a difference in the pro- 
portion of the energy utilized may be caused by a difference in the 
digestive work; in other words, that it is the availability that is 
modified rather than the proportion of the available energy which is 
recovered as gain. While not denying that the latter function may 
be also modified, either directly as the effect of varying amounts 
of food, or indirectly by changes in the chemical nature of the sub- 
stances resorbed from the digestive tract under varying conditions 
of fermentation, it seems probable that the main effect is that upon 
availability. 

It is to be observed that the rations used in these experiments, 
while not heavy fattening rations, still produced very fair gains. 
The experimental periods were comparatively short and hence 
the testimony of the live weight itself is liable to be misleading. 
Taking the actual gains of fat and proteids as shown by the respi- 
ration experiments, however, and comparing them with the compo- 
sition of the increase of live weight in fattening as determined by 
Lawes & Gilbert, it appears that the total gain per day was equiva- 
lent to from 0.9 to 2.5 pounds gain in live weight per day in the ex- 
periments on coarse fodder, while in those upon concentrated feeds 
the corresponding range is from 1 to 3 pounds. 



THE UTILIZATION OF ENERGY. 47 1 

It may be remarked further that the rations in Kiihn's experi- 
ments differed materially from those ordinarily used in practice, 
both as to their make-up and their very wide nutritive ratio, so 
that the conditions may fairly be regarded as in a sense abnormal. 
Kellner's rations represent more nearly normal conditions, and 
they fail, as we have seen, to give any clear indications of an in- 
fluence of amount of food upon the proportion of energy utilized. 
Whether other feeding materials show a behavior analogous to that 
of starch, future investigations must decide. In the meantime 
we are apparently justified in discussing such results as are now 
on record upon the provisional hypothesis that, within reasonable 
limits, the utilization of energy is independent of the amount of 
food, or, in other words, is a linear function. 

Influence of Thermal Environment. — The influence of the 
thermal environment of the animal upon its heat production and 
upon the net availability of the energy of the food has already been 
fully discussed in previous pages and needs only a brief consider- 
ation here. 

Ruminants. — We have already found reason to think that in 
ruminants the heat production on the ordinary maintenance ration 
is in excess of the needs of the body. Kiihn's and Kellner's results 
show us that from 25 to 72 per cent, of the metabolizable energy 
of the food supplied in excess of the maintenance requirement was 
converted into heat, so that the heat production was frequently 
increased 40 or 50 per cent, above that which was observed on the 
maintenance ration. Under these circumstances we can hardly 
suppose that any moderate changes in the thermal environment 
would sensibly affect either the availability of the food energy or its 
percentage utilization. 

The writer is not aware of any exact determinations of the 
influence of the thermal environment upon the heat production of 
fattening ruminants, but the above conclusion is in harmony with 
the practical experience of many feeders that moderate exposure 
to cold is no disadvantage, but rather an advantage in maintaining 
the health and appetite of the animals, and it appears also to have 
the support of not a few practical feeding trials.* 

* Compare Henry, " Feeds and Feeding," -second edition, p. 364, and 
Waters, Bulletin Mo. Bd. Agr., September, 1901, p. 23. 



47 2 PRINCIPLES OF ANIMAL NUTRITION. 

Naturally this can be true only within limits, and exposure to 
very low temperatures, especially in a damp climate, and particu- 
larly to cold rains, causing a large expenditure of heat in the evapo- 
ration of water from the surface of the body, may very well pass 
the limit and cause an increase in the metabolism simply to main- 
tain the temperature of the body. Finally, the time element, as 
pointed out on p. 439, is one to be taken into consideration. 

Swine. — As was remarked on p. 435, the work of digestion is 
doubtless less with the swine than in ruminants, on account of the 
more concentrated nature of his food, and as was shown on p. 438, 
the maintenance requirement appears to be affected by the thermal 
environment. The same reason would tend to make fattening 
swine more susceptible to this influence than fattening ruminants. 
This conclusion is borne out by the experiments of Shelton * at the 
Kansas Agricultural College, who found that swine kept in an open 
yard during rather severe weather required 25 per cent, more corn 
to make a given gain than those sheltered from extreme cold. 

Influence of Character of Food. — Attention was called in the 
previous chapter to the fact that the expenditure of energy in the 
digestion and assimilation of the food is largely dependent upon the 
nature of that food, but as was there pointed out, we have few 
quantitative determinations of the differences. Experiments of 
the class now under consideration show marked variations in the 
proportion of tne metabolizable energy of different foods which 
is utilized, and we should naturally be inclined to ascribe these 
variations to differences in the work of digestion and assimilation 
rather than to differences in the physiological processes involved 
in tissue production. 

The data recorded in the foregoing pages constitute only a 
beginning of the study of the utilization of the energy of feeding- 
stuffs, but a brief consideration of the main results will prove at 
least suggestive. 

Concentrated Feeding-stuffs. — As we saw in connection 
with the discussion of the metabolizable energy of feeding-stuffs in 
Chapter X, the Mockern experiments, to which we owe the larger 
share of our present knowledge regarding the metabolism of energy 
in farm animals, were made for the purpose of comparing the 
* Rep. Prof, of Agriculture, 1883. 



THE UTILIZATION OF ENERGY. 473 

principal classes of nutrients rather than commercial feeding-stuffs. 
Accordingly such representative materials as starch, oil, and glu- 
ten were largely used, and we have as yet but few determinations 
either of the metabolizable energy of ordinary concentrated feeding- 
stuffs or of its percentage utilization. We have already considered 
to some extent the advantages and disadvantages resulting from 
making the pure nutrients, on the one hand, or actual feeding-stuffs, 
on the other, the starting-point for investigations. Passing over 
this question for the present, we may conveniently group together 
here such results as are on record for materials other than coarse 
fodders. 

Starch. — Starch, as a representative of the readily digested car- 
bohydrates, has, as we have seen, received a large share of atten- 
tion. The results obtained are tabulated in the Appendix, and 
have already been partially considered in their bearings upon the 
influence of amount of food. It was there noted that the earlier 
series of experiments by Kuhn, in which the starch was added to 
a ration of coarse fodder only, gave results differing decidedly from 
those obtained later by Kellner from the addition of starch to a 
mixed fattening ration. Among the latter experiments, more- 
over, were two (animals B and C) which were exceptional in that 
very large total amounts of starch were contained in the ration, 
relatively large amounts escaping digestion, while none of the added 
starch underwent the methane fermentation. 

A clear image of the fate of the total potential energy supplied 
to the organism in the starch is best obtained by a study of its per- 
centage distribution among the several excreta, the work of digestion, 
assimilation, and tissue building, and the gain secured, as in the 
table on page 474, in which each of the three sets of experiments 
indicated above is given separately. The figures for the work of 
digestion, etc., are, of course, obtained by difference. 

As pointed out in the discussion of metabolizable energy, the 
percentage of the gross energy carried off in the feces includes, as 
here computed, not only the energy of the undigested portion of the 
starch itself, but also that of the portion of the basal ration which 
escaped digestion under the influence of the starch. This is espe- 
cially true of Kellner's experiments with moderate rations, in which 
little or no starch could be detected in the feces. Similarly, the 



474 



PRINCIPLES OF ANIMAL NUTRITION. 



PERCENTAGE DISTRIBUTION OF GROSS ENERGY OF STARCH. 



Kiihn's experiments. 



Kellner's experiments: 
Moderate rations. . . . 



Kellner's experiments: 
Heavy rations 



Averages : 

Kuhn's experiments . 
Kellner's experiments: 

Moderate rations. . . 

Heavy rations 



Ill 

IV 

V 

V 

VI 

VI 

D 

F 

G 

H 

J 

B 
C 



2 
2 

2a 

2b 

20 

3 

2 

4 

4 

3 

3 

2 
2 



In 
Feces. 



20.02 
25.29 
8.82 
15.73 
22.49 
19.03 
29.99 
16.42 
13.35 
15.72 
14.85 

59.60 
52.22 

19.59 

17.61 
55.91 



In 
Urine. 



-1 



.29 

■1.01 
1.03 
■0.27 
2.61 
■0.88 
3.27 
0.73 
0.35 
■2.32 
1.14 

-3.25 

-0.89 

-0.92 

-0.66 
-2.07 



10.06 

12.01 

11.20 

9.86 

8.86 

11.87 

6.08 

11.41 

8.98 

7.38 

11.85 

-4.96 
-0.01 

10.74 

9.21 
-2.49 



Work of 
Diges- 
tion, 
Assimi- 
lation, 
and 
Tissue 
Build- 
ing. 



35.61 
32.41 
36.95 
34.58 
36.96 
37:38 
31.10 
25.24 
26.42 
34.82 
32.66 

16.82 
26.68 

35.19 

30.64 
18.75 



In 
Gain. 



35.60 
31.30 
42.00 
40.10 
34.30 
32.60 
36.10 
46.20 
50.90 
44.40 
39.50 

31.80 

28.00 

35.40 

43.20 
29.90 



negative losses in the urine and, in two cases, in the methane 
mean, of course, that under the influence of starch the metabolic 
or other processes were so modified that less of the potential energy 
of the basal ration was lost through these channels. The starch, 
so to speak, borrowed energy from the basal ration. In brief, the 
figures of the table give us a picture of the aggregate net results of 
supplying 100 units of additional potential energy in the form of 
starch, or in other words, of the "apparent" utilization. 

As between Kuhn's results and those of Kellner upon moderate 
rations, the chief difference, as already noted, is the less evolution 
of methane in the latter and, apparently as, in part, a consequence 
of this, the smaller expenditure of energy in the work of digestion, 
etc. Combined with the slightly smaller loss in the feces, this 
results in making the energy utilized a much larger percentage of 
the gross energy. Apparently Kellner's figures correspond most 
nearly to normal conditions of feeding and may be taken to repre- 
sent the average utilization of starch under these circumstances. 



THE UTILIZATION OF ENERGY. 



475 



In Kellner's two experiments on heavy rations the enormous losses 
in the feces cut down the percentage utilization to a very low 
figure and thus render difficult a direct comparison with the 
other averages. 

While the above form of stating the results appears the simplest 
and most direct , it is of interest also to eliminate the influence of 
varying digestibility by computing the percentage distribution 
of the gross energy of the apparently digested portion of the starch. 
This is particularly the case since Kellner's computations of his 
experiments are made in a somewhat similar way. Combining 
the data given on p. 461, regarding the percentages of metaboliz- 
able energy utilized, with those on p. 301 for the energy of the 
apparently digested matter, we have the following: 



DISTRIBUTION OF ENERGY OF APPARENTLY DIGESTED STARCH. 



In Urine. 
Per Cent. 



In Methane. 
Per Cent. 



Work of 

Digestion, 

Assimilation, 

and Tissue 

Building. 

Per Cent. 



In Gain. 
Per Cent. 



Kiihn's experiments . 
Kellner's experiments 

Moderate rations . . 

Heavy rations 



-1.19 

-0.92 
-4.95 



13.42 

11.12 
-6.15 



43.89 

37.36 

42.77 



43.88 

52.44 
68.33 



Kellner's computations are made in a different manner.* Omit- 
ting in the computation of metabolizable energy the correction for 
nitrogen gained or lost, he compares the period in which starch was 
fed with that on the basal ration substantially as has been done 
above. He then, however, introduces a correction for the influence 
of the starch upon the digestibility of the basal ration. For ex- 
ample, comparing Periods 3 and 4 on Ox H, he finds in the manner 
shown on p. 307, Chapter X, that the equivalent of 820 Cals. less 
of the basal ration was digested in the period in which starch was 
added to it, while there is a further correction of 112 Cals. to be 
made for the less amount of organic matter of the basal ration con- 
sumed in Period 3, making a total difference of 932 Cals. Of the 
gross energy of the basal ration, 79.9 per cent, was found to be met- 



* Compare Landw. Vers. Stat., 53, 450. 



476 



PRINCIPLES OF ANIMAL NUTRITION. 



abolizable, so that the above difference in gross energy would corre- 
spond to 745 Cals. of metabolizable energy. Of the metabolizable 
energy of the basal ration in excess of maintenance, 59.6 per cent, 
was recovered in the gain. If, then, the differences in organic matter 
consumed and in the digestibility of the basal ration had not offset 
some of the effect of the starch in Period 3, there would have been 
745 Cals. more of metabolizable energy disposable from the basal 
ration, and presumably the gain resulting from this would have been 
59.6 per cent, of 745 Cals., or 444 Cals. We have, then, by this 
method the following: 




Energy of 
Gain, 
Cals. 



Period 3 minus Period 4.. . 
Correction for live weight. 



Correction for organic matter and for decreased 
digestibility 



Percentage utilization 



3752 
40 

3712 

444 

4156 
56. 6£ 



Kellner's results, then, assuming that the corrections are accu- 
rate, represent respectively the metabolizable and the utilizable 
energy of the digested matter of the starch itself, while the results 
as computed on the preceding pages represent, as was there pointed 
out, a balance between the various negative and positive effects of 
the addition of starch. In other words, Kellner attempts to com- 
pute the real as distinguished from the apparent utilization of the 
energy of the starch. The comparison on the opposite page of the 
percentages obtained in this way with those computed on p. 461 
will therefore be of interest. 

Kellner also computes by his method the distribution of the 
gross energy of the digested starch in Kiihn's experiments and in his 
own experiments on moderate rations. As calculated in Chapter X, 
pp. 325-6, the average loss of potential energy in methane was 12.7 
per cent, in Kuhri's experiments, and 10.11 per cent, in Kellner's, 
while none of the potential energy of the digested starch passed 



THE UTILIZATION OF ENERGY. 



477 



UTILIZATION OF METABOLIZABLE ENERGY OF STARCH. 



Kilhn's experiments 



Kellner's experiments : 
Moderate rations. . . 



Heavy rations 

Averages . 

Kuhn's experiments . . 
Kellner's experiments: 

Moderate rations. . . 

Heavy rations 



Animal 



III 

IV 

V 

V 

VI 

VI 

D 
F 
G 
H 
J 
B 
C 



Period. 



2 

2 

2a 

2b 

26 

3 

2 
4 
4 
3 
3 
4 
2 



Real Utiliza- 
tion as 

Computed by 
Kellner. 
'"■sr Cent. 



46.2 
49.0 
51.3 
52.6 
48.0 
46.8 



54 
63 
65 
56 
55 
61 



56.4 

49.0 

58.9 
58.9 



Apparent 

Utilization as 

Computed on 

p. 461. 

Per Cent. 



50.0 
49.2 
53.2 
53.7 
48.1 
46.6 

53.7 

64.8 
65.8 
56.0 
54.8 
65.4 
57.6 

50.0 

58.4 
61.5 



into the urine. In the two cases, then, 87.30 per cent, and 89.89 
per cent, respectively of the potential energy of the digested starch 
was metabolizable. Of this metabolizable energy 49.0 per cent, 
and 58.9 per cent, respectively was recovered in the gain. Com- 
bining these figures we have — 



DISTRIBUTION OF ENERGY OF DIGESTED STARCH. 



In Urine 
Per Cent. 



In Methane 
Per Cent. 



Work of 
Digestion . 
Assimilation, 
and Tissue 
Building 
Per Cent. 



In Gain 
Per Cent. 



Kuhn's experiments . . . 

Kellner's experiments; 

Moderate rations 



12.70 
10.11 



44.52 
36.95 



42.78 
52.94 



The final results for the energy recovered in the gain of tissue, 
whether expressed as a percentage of metabolizable energy or of 
energy of digested matter, are substantially the same numer- 
ically as those reached by the former method of computation, but 
this agreement is purely accidental, and the significance of the 



473 



PRINCIPLES OF ANIMAL NUTRITION. 



figures is essentially different, as already explained. From the re- 
sults last given, assuming the gain of energy to have been entirely 
in the form of fat, Kellner * computes that the conversion of starch 
into fat in cattle takes place according to the following scheme : 

Starch 100.00 grams 

+ Oxygen 38.69 " 

Yield: 

Methane 3.17 grams 

Water 23.40 " 

Carbon dioxide 88. 78 " 

Fat 23.34 " 



138.69 grams 138.69 " 

Oil. — Applying to Kellner's three experiments upon the addition 
of oil to a basal ration the same method of computation which was 
used for the starch — that is. computing the apparent utilization — 
we have the results shown in the two following tables : 

DISTRIBUTION OF GROSS ENERGY OF OIL. 





"3 

a 
■a 
< 


•6 
.2 


In Feces. 
Per Cent. 


In Urine. 
Per Cent. 


In 
Methane. 
Per Cent. 


Work of 
Digestion. 
Assimila- 
tion and 

Tissue 
Building. 
Per Cent. 


In Gain. 
Per Cent. 


Sample I 


D 
F 
G 


3 
5 

5 


24.34 
64.77 
41.00 
52.89 


-1.08 

-1.19 

1.37 

0.09 


- 1.02 
-16.10 
-1.76 

- 8.93 


37.66 
18.32 
18.19 
18.25 


40.10 


" II 

Average of Sample 


! 

11 


34.20 
41.20 
37.70 









DISTRIBUTION OF ENERGY OF APPARENTLY DIGESTED OIL. 



Sample I 

II... -j 

Average lor Sample II 



Animal. 



Period. 



In Urine. 
Per Cent, 



■1.42 
-3.38 
2.32 
-0.53 



In 
Methane 
Per Cent. 



- 1.34 
-45.69 
-3.01 

-24.35 



Work of 
Digestion 
Assimila- 
tion and 

Tissue 
Building 
Per Cent. 



49.76 
52 . 01 
30.83 
41.42 



In Gain. 
Per Cent. 



53 . 00 
97.06 
69.86 
83.46 



* Loc. cit., 53, 452. 



THE UTILIZATION OF ENERGY. 



479 



As was noted in the discussion of metabolizable energy in 
Chapter X, the results on Ox F appear to be exceptional, but those 
upon the other two show considerable differences, and it is evident 
that further investigation will be necessary to obtain satisfactory 
data upon the effect of oil fed in this way. 

Kellner's method of computation, based upon the provisional 
conclusion on p. 323, Chapter X, that oil has substantially no effect 
upon the loss of energy in urine and methane under normal condi- 
tions, gives the following results: 



PERCENTAGE OP METABOLIZABLE ENERGY UTILIZED. 





As Computed 
by Kellner. 


As Computed 
on p. 462. 


Ox D . 

" F 


52.2 


51.6 
65.1 
69.4 


" G 


59.4 





DISTRIBUTION OF ENERGY OF DIGESTED OIL. 





Ani- 
mal. 


Period. 


In Urine, 
Per Cent. 


In Methane, 
Per Cent. 


Work of 
Digestion, 
Assimilation 
and Tissue 
Building, 
Per Cent. 


In Gain, 
Per Cent. 


" II 


D 
G 


3 
5 










47.8 
40.6 


52.2 
59.4 


Average 



0.5 



-2.2 


44.2 
40.3 


55 8 


Average computed 






61 4 











The numerical results of these experiments show more clearly 
than was the case with the starch the difference in the two methods of 
computation. Both methods agree, however in showing that the 
combined expenditure of energy in the digestion and assimilation of 
the oil and in tissue building is very considerable. We have already 
seen that the expenditure of energy in the digestion of fat by cai- 
nivora and by man is comparatively small. If we are justified in 
assuming that the same thing is true of ruminants, the result just 
reached signifies that the digested fat undergoes extensive trans- 
formations before being finally deposited in the adipose tissue. 



480 



PRINCIPLES OF ANIMAL NUTRITION. 



Until, however, we have satisfactory determinations of the per- 
centage utilization of fat by carnivora, or of its net availability 
in ruminants, or both, no final conclusion on this point is possible. 
Wheat Gluten. — The three samples of this feeding-stuff experi- 
mented upon contained respectively 87.88, 83.45, and 82.67 per 
cent, of crude protein in the dry matter, the remainder being 
chiefly starch, with the exception of 2.22 per cent, of ether 
extract in the first lot. A reference to the results obtained for 
the metabolizable energy will show that they were variable and 
also that, especially in the earlier experiments, the incidental 
effects were large. Tabulating the results as in case of starch 
and oil we have the results contained in the tables on this and 
the opposite pages. 



DISTRIBUTION OF GROSS ENERGY OF WHEAT GLUTEN. 



Kuhn's experiments. . ^ 

Kellner's experiments.' 

Sample I ,> 

I 

Sample II 

Average of 1 and II. 



Ill 
111 

Av. 
IV 

B 
B 

C 

Av. 
D 



In Feces. 
Per Cent. 



-10.38 
- 1.28 



- 5.83 

-16.17 

30.16 
22.55 
20.89 



24.53 
15.80 
20.16 



In 

Urine. 

Per Cent 



17.85 
21.71 



19.78 
16.18 

16.58 
13.52 
11.19 



13.76 
12.39 
13.08 



In 
Methane. 
Per Cent. 



Work of 
Diges- 
tion. 
Assimila- 
tion, and 
Tissue 
Building. 
Per Cent. 



10.81 
5.08 



7.95 
-1.26 

0.08 
-1.62 
-3.69 



-1.74 
1.91 

0.08 



44.72 
38.69 



41.70 
42.35 

33.58 
32.95 
40.71 



35.75 

43. SO 
39.78 



In Gain. 
Per Cent. 



37.00 
35.80 



36.40 
58.90 

19.60 
32.60 
30.90 



27.70 
26.10 
26.90 



The exceptionally small loss of energy in the urine in the case 
of Ox IV, Period 3, and the total suppression of the methane fer- 
mentation, as well as the fact that the metabolizable energy was 
apparently greater than the gross energy, seem to justify exclud- 
ing this experiment from the average, although there was appar- 
ently nothing abnormal in the ration fed. In the experiment 
with Ox D, Period 4, the nutritive ratio was very narrow 
(1 g 3.3), and Kellner considers this a probable explanation of the 



THE UTILIZATION OF ENERGY. 



481 



DISTRIBUTION OF ENERGY OF APPARENTLY DIGESTED MATTER. 















Work of 
















Digestion, 








"3 

S 


T3 

.2 


In Urine. 
Per Cent. 


In 

Methane. 
Per Cent. 


Assimila- 
tion, and 
Tissue 


In Gain. 
Per Cent. 






% 


O, 






Building. 
Per Cent. 






r 


III 


3 


16.17 


9.79 


40.50 


33.54 






111 


4 


21.44 


5.02 


38.24 


35.30 




> 
























1 


Av. 




18.81 


7.39 


39.38 


34.42 




1 


IV 


3 


13.92 


-1.07 


36.44 


50.71 


Kellner's experiments: 


















\ 


B 


1 


23.74 


0.11 


48.06 


28.09 




1 


B 


3 


17.46 


-2.10 


42.57 


42.07 




1 
1 


'C 

Av 


3 


14.15 


-4.67 


51.46 


39.06 




18.45 


-2.22 


47.35 


36.42 


Sample II 




D 


4 


14.72 


2.27 


52.01 


31.00 


Average of I and II. . 








16.59 


0.02 


49.68 


33 71 











relatively small utilization of the protein as computed by his 
method. (See below.) An unexpected result is that while the 
earlier sample of gluten seems to have increased the methane 
fermentation, the later samples, although containing more starch, 
caused a decrease in the methane production except in case of 
OxD. 

Digestible Protein. — Kellner does not attempt to compute the 
energy utilized from the wheat gluten as a whole by his method, but 
uses the results as a basis for computing the utilization of the energy 
of the digested protein. He finds that of the metabolizable energy 
of the latter, computed in the manner described in Chapter X 
(p. 316). the following percentages were recovered in the gain: 

Ox B 45 . per cent. 

Ox C 42 . 7 

Ox III 45.1 

Ox IV 48.8 



Average 45 . 2 

OxD 32.9 



The average loss of energy in the urine was found (p. 317) to be 
19.3 per cent, of the gross energy of the digested protein. Applying 



4»2 



PRINCIPLES OF ANIMAL NUTRITION. 



this average to the above figures, and assuming with Kellner that 
the protein does not take part in the methane fermentation, we 
have the following: 



DISTRIBUTION OF ENERGY OF DIGESTED PROTEIN. 



Animal. 


In Urine. 
Per Cent. 


In Methane. 
Per Cent. 


Woik of 
Digestion. 
Assimilation 
and Tissue 
Building. 
Per Cent 


In Gain. 
Per Cent 


13 




- 19.30 


- 




44.38 
46.24 
44.30 
41.32 


36.32 


c 


34.46 


Ill 


36.40 


IV 


39.28 






Average .... 
D 


44.07 
54.15 


36.63 
26.55 















There is a wide discrepancy between these results and those 
computed on p. 465 from the experiments of Kern & Wattenberg 
upon sheep with conglutin and flesh-meal, Omitting the apparently 
exceptional result of Period II we have the following as the per- 
centages of the (computed) metabolizable energy of the digested 
proteids which was utilized in those experiments: 



Conglutin \ 

Average 

Flesh-meal -j 

Average 



Period. 



Ill 



V 
VI 



Per Cent 



67.63 
67.76 

67 70 

60.59 
69.33 

64.96 



While the gain in these cases includes a considerable growth 
of wool, it seems difficult to suppose that this alone can have made 
the conditions so much more favorable for the storing up of the 
added protein as to account for the great difference between these 
results and Refiner's, and it must apparently be left to further 
investigation to clear up the matter. 



THE UTILIZATION OF ENERGY. 



483 



It need hardly be added that none of these results are directly 
comparable with those computed above, after another method, for 
the wheat gluten as a whole. 

Beet Molasses. — The results of the three experiments upon beet 
molasses show such great differences, as was noted in Chapter X 
and as is further apparent from the following table, that any dis- 
cussion of them would evidently be premature: 

DISTRIBUTION OF GROSS ENERGY OF BEET MOLASSES. 





"3 

a 
■3 
< 


-6 


0) 


In Feces. 
Per Cent. 


In Urine. 
Per Cent. 


In 
Methane. 
Per Cent. 


Work of 
Digestion, 
Assimilation, 
and Tissue 
Building. 
Per Cent. 


In Gain. 
Per Cent. 


" 11 1 


F 
H 
J 


6 
6 
6 


26.87 

5.40 

14.45 


3.92 
3.16 
2.67 


-1.95 
12.44 
10.18 


29.56 
13.10 
36.20 


41.60 
65.90 
36.50 


Average 


9.92 


2.92 


11.31 


24.65 


51 20 











Rice. — The two experiments upon swine by Meissl, Strohmer & 
Lorenz, when computed as on p. 454, show that of the (estimated) 
metabolizable energy of the food approximately the following per- 
centages were recovered in the gain: 

Period 1 80 . 7 per cent. 

" II 75*2 " " 

Average 78.0 " " 

These results are notably higher than any obtained in experi- 
ments on ruminants. Like the results on barley and cockle below 
they are the expression in another form of the well-known supe- 
riority of the swine as an economical producer of meat. 

Barley. — For the utilization of the energy of this grain the 
single experiment by Meissl, Strohmer & Lorenz gives 70.9 per cent, 
of the (estimated) metabolizable energy. 

Mixed Grains. — For mixed grains Kornauth & Arche's results 
on swine give figures which do not differ materially from the result 
just computed for barley, viz.: 

Experiment II 71.7 per cent. 

Ill 65.3 " " 



484 



PRINCIPLES OF ANIMAL NUTRITION. 



Coarse Fodders. — Kellner's results upon hay, straw, and ex- 
tracted straw are the only data regarding the utilization of the 
energy of this class of feeding-stuffs which we as yet possess. Only 
those experiments in which coarse fodder was added to a mixed 
basal ration are available for a computation of this sort. 

Meadow Hay. — The two kinds of meadow hay (V and VI) used 
in Kellner's experiments gave the following results for the distri- 
bution of their energy, computed as in previous instances : 

DISTRIBUTION OF GROSS ENERGY OF MEADOW HAY. 



In 

Feces. 
Per Cent. 



In 

Urine. 

Per Cent. 



In 

Methane . 
Per Cent. 



Work of 
Digestion, 
Assimila- 
tion, and 

Tissue 
Building. 
Per Cent. 



In Gain. 
Per Cent. 



Sample V. 



Sample VI . 



Average of V and VI . 



F 
G 

Av. 

H 
H 
J 

Av. 



49.81 
44.80 



4.32 

4.26 



5.12 
6.94 



24.25 
28.10 



47.30 

37.07 
34.78 
34.30 



4.29 

5.24 
5.00 
6.33 



6.03 

4.87 
6.15 
6.13 



26.18 

26.32 

27.97 
34.74 



35.38 
41.34 



5.52 
4.91 



5.72 

5.87 



29.68 
27.93 



16.50 
15.90 



16.20 

26.50 
26.10 
18.50 



23.70 
19.95 



DISTRIBUTION OF ENERGY OF APPARENTLY DIGESTED MATTER. 





"3 

a 

'3 
< 



't- 


In Urine. 
Per Cent. 


In 
Methane. 
Per Cent. 


Work of 
Digestion, 
Assimila- 
tion, and 

Tissue 
Building. 
Per Cent. 


In Gain. 
Per Cent. 


r 

Sample V J 


F 
G 

Av. 

H 
H 

J 

Av. 


1 

2 

2 
7 
2 


8.61 

7.72 


10.20 
12.58 


48.39 
50.85 


32.80 

28.85 


1 


8.17 

8.32 
7.66 
9.64 


11.39 

7.74 
9.43 
9.33 


49.62 

41.63 

42.77 
52.83 


30.82 

42.31 

40.14 

28.20 


I 
Average of V and VI. . 


8.54 
8.34 


8.83 
10.78 


45.75 
49.08 


36.88 
31.80 











THE UTILIZATION OF ENERGY. 



485 



Computed by Kellner's method, the percentage of the metabo- 
lizable energy of the hay which was recovered as gain of tissue was 
as follows, as compared with the results obtained by the writer's 
method : 



PERCENTAGE OF METABOLIZABLE ENERGY RECOVERED. 







Computed by 
Kellner's 
Method. 


Computed by 

the Writer's 

Method. 


r 


Ox F 


42.8 
37.7 


40 4 


Hav V 


" G 


36.2 




Average 




I 


40.2 

i 49.9 j 

35.8 


38 3 


Hay VI \ 

1 


OxH, Period 2.... 
" H, " 7 ... 
" J 

Average 


50.4 

48.4 
34.8 


I 
Average of V and VI .... 


42.8 
41.5 


44.5 
41 4 









Computing the results upon the gross energy of the digested 
matter of the hay, Kellner obtains the following: 



DISTRIBUTION OF ENERGY OF DIGESTED MATTER. 





In Urine. 
Per Cent. 


In Methane. 
PerCent. 


Work of 
Digestion, 
Assimilation, 
and Tissue 
Building. 
Per Cent. 


In Gain. 
Per Cent. 


Hay V 


8.2 

8.8 


11.5 
9.0 


48.00 
48.10 


32.3 


" VI 


34.1 






Average 


8.5 


10.3 


48.00 


33.2 







As in some previous cases, the numerical results of the two 
methods of computation do not vary greatly, but their essentially 
different significance should not be forgotten. 

Oat Straw. — For the single sample of this feeding-stuff experi- 
mented on, the results, arranged in the same order as before, were 
as follows: 



486 



PRINCIPLES OF ANIMAL NUTRITION. 



DISTRIBUTION OF GROSS ENERGY OF OAT STRAW. 



Animal. 


Period. 


In Feces. 
Per Cent. 


In Urine. 
Per Cent. 


In 
Methane. 
Per Cent. 


Work of 
Digestion, 
Assimila- 
tion, and 

Tissue 
Building. 
Per Cent. 


In Gain. 
Per Cent. 


F 


2 
1 


56.77 

56.86 


2.29 
1.86 


4.40 
6.23 


22.34 
23.35 


14.20 


G 


11.70 






Average 


56.81 


2.08 


5.31 


22.85 


12.95 









DISTRIBUTION OF ENERGY OF APPARENTLY DIGESTED MATTER. 



Animal. 


Period. 


In Urine. 
Per Cent. 


In Methane. 
Per Cent. 


Work of 
Digestion, 
Assimilation, 
and Tissue 
Building. 
Per Cent. 


In Gain. 
Per Cent. 


F 


2 
1 


5.30 
4.32 


10.17 
14.42 


51.73 
54.12 


32.80 


G 


27.14 






Average 


4.81 


12.30 


52.92 


29.97 









PERCENTAGE OF METABOLIZABLE ENERGY RECOVERED. 





Computed by 
Kellner's Method. 


Computed by the 
Writer's Method. 


Ox F 


39.9 
35.3 


38.8 
33.4 


" G 


Average 


37.6 


36.1 



DISTRIBUTION OF ENERGY OF DIGESTED MATTER (KELLNER). 





In Urine. 
Per Cent. 


In Methane. 
Per Cent. 


Work of 
Digestion, 
Assimilation, 
and Tissue 
Building. 
Per Cent. 


In Gain. 
Per Cent. 


Average F and G. . . 


.4.7 


12.2 51.9 

I 


31.2 



THE UTILIZATION OF ENERGY. 



487 



Wheat Straw. — Tabulating the results upon wheat straw in the 
same manner as those for oat straw we have — • 



DISTRIBUTION OF GROSS ENERGY OF WHEAT STRAW. 



Animal. 


Period. 


In Feces. 
Per Cent. 


In Urine. 
Per Cent. 


In 

Methane. 
Per Cent. 


Work of 
Digestion, 
Assimila- 
tion, and 

Tissue 
Building. 
Per Cent. 


In Gain. 
Per Cent. 


H 


1 
1 


60.41 
56.03 


1.88 
2.85 


7.96 
8.65 


26.55 
24.67 


3.20 


J 


7.80 






Average . . . 


58.21 


2.37 


8.31 


25.61 


5 50 









DISTRIBUTION OF ENERGY OF APPARENTLY DIGESTED MATTER. 



Animal. 


Period. 


In Urine. 
Per Cent. 


In Methane. 
Per Cent. 


Work of 

Digestion, 

Assimilation, 

and Tissue 

Building. 

• Per Cent. 


In Gain. 
Per Cent. 


H 

J 


1 
1 


4.75 
6.49 


20.11 
19.67 


67.03 
56.12 


8.11 
17.72 






Average 


5.62 


19.89 


61.57 


12.92 









PERCENTAGE OF METABOLIZABLE ENERGY RECOVERED. 





Computed by 
Kellner's Method. 


Computed by the 
Writer's Method. 


Ox H 


11.2 
24.3 


10.8 
24.0 


" J 




17.8 


17.4 



DISTRIBUTION OF ENERGY OF DIGESTED MATTER (KELLNER). 

Average of 
H and J. 

In urine 5.6 

In methane 20 . 

Work of digestion, assimilation, and tissue building. 61 .2 

In gain 13.2 

100.0 



488 



PRINCIPLES OF ANIMAL NUTRITION. 



Extracted Straw. — As previously noted in another connection,, 
this material consisted of rye straw which had been treated with an 
alkaline liquid under pressure, substantially as in the manufacture 
of straw paper. It contained in the water-free state 76.78 per cent, 
of crude fiber and 19.96 per cent, of nitrogen-free extract. Con- 
siderable interest attaches to the results obtained upon this sub- 
stance as representing to a degree the crude fiber of the food of 
herbivorous animals. Computed as before, these results were: 

DISTRIBUTION OF GROSS ENERGY OF EXTRACTED STRAW. 



Animal. 


Period. 


In Feces. 
Per Cent. 


In Urine. 
Per Cent. 


In 
Methane. 
Per Cent. 


Work of 
Digestion, 
Assimila- 
tion, and 

Tissue 
Building. 
Per Cent. 


In Gain. 
Per Cent. 


H 


5 
5 


11.35 
14.14 


-0.46 
-1.11 


12.40 
12.52 


25.11 
30.85 


51.60 


J 


43.60 






Average .... 


12.75 


-0.79 


12.46 


27.98 


47.60 









DISTRIBUTION OF ENERGY OF APPARENTLY DIGESTED MATTER. 



Animal. 


Period. 


In Urine. 
Per Cent. 


In Methane. 
Per Cent. 


Work of 
Digestion, 
Assimilation, 
and Tissue 
Building. 
Per Cent. 


In Gain. 
Per Cent. 


H 


5 
5 


-0.52 
-1.29 


13.99 
14.58 


28.29 
35.89 


58.24 


J 


50.82 






Average 


-0.91 


14.29 


32.09 


54.53 









PERCENTAGE OF METABOLIZABLE ENERGY RECOVERED. 





Computed by 
Kellner's Method. 


Computed by the 
Writer's Method. 


Ox H 


67.5 

58.7 


67.3 

58.6 


" J 

Average 


63.1 


63.0 



THE UTILIZATION OF ENERGY. 



489 



DISTRIBUTION OF ENERGY OP DIGESTED MATTER (KELLNER). 

Average of 
H and J. 

In urine 0.0 

In methane 14.0 

Work of digestion, assimilation, and tissue building. 31.7 

In gain 54 . 3 



100.0 



As was noted in discussing the results upon metabolizable 
energy, the treatment to which the straw was submitted left 
it in a condition in which its digestibility, and consequently its 
percentage of metabolizable energy, compared favorably with that 
of starch. As we now see, this analogy extends also to its effect 
in producing gain, the figures showing in this respect a slight 
superiority on the part of the extracted straw, as appears from 
the following summary: 

RECOVERED IN GAIN. 



Starch (Kellner's 

Experiments on 

Moderate 

Rations). 



Extracted Straw. 



Per cent, of gross energy 

" " " apparently digested energy . 
" " " metabolizable energy 



43.4 
53.1 
59.0 



47.6 
54.5 
63.0 



The reason for this strikingly high value of the extracted straw 
as compared with the low value indicated for crude fiber by the 
results of Zuntz and Wolff will be considered in a subsequent para- 
graph. 

Summary. — For convenience of reference the foregoing results 
may be summarized in the tables on pages 490 and 491, 
showing respectively the percentage distribution of the gross 
energy of the feeding-stuffs, that of the energy of the appar- 
ently digested organic matter, and the percentage utilization of 



49° 



PRINCIPLES OF ANIMAL NUTRITION. 



the metabolizable energy according to the two methods of com- 
putation adopted: 

DISTRIBUTION OF GROSS ENERGY. 











Work of 












Diges- 






In 


In 


In 


tion, As- 


In 




Feces. 


Urine. 


Methane. 


simila- 


Gain. 




Per Cent. 


Per Cent. 


Per Cent. 


tion, and 

Tissue 

Building. 

Per Cent. 


Per Cent. 


Concentrated. Feeding-stuffs : 












Starch, Kuhn's experiments .... 


19.59 


-0.92 


10.74 


35.19 


35.40 


" Kellner's experiments, 












moderate rations 


17.61 


-0.66 


9.21 


30.64 


43.20 


heavy rations.. . 


55.91 


-2.07 


-2.49 


18.75 


29.90 




52.89 


0.09 


-8.93 


18.25 


37.70 


Wheat gluten, Kellner's expts . . 


20.17 


13.08 


0.08 


39.78 


26.90 


Beet molasses, Sample II 


9.92 


2.92 


11.31 


24.65 


51.20 


Coarse Fodders : 














41.34 
56.81 
58.21 
12.75 


4.91 

2.08 

2.37 

-0.79 


5.87 

5.31 

8.31 

12.46 


27.93 

22.85 
25.61 

27.98 


19.95 




12.95 


Wheat straw 


5.50 




47.60 











DISTRIBUTION OF ENERGY OF APPARENTLY DIGESTED MATTER. 



Concentrated Feeding-stuffs : 

Starch, Kuhn's experiments 

" Kellner's experiments, moder- 
ate rations 

" Kellner's experiments, heavj 

rations 

Oil, Sample II 

Wheat gluten, Kellner's experiments. . . 

Coarse Fodders : 

Meadow hay 

Oat straw 

Wheat straw 

Extracted straw 



In 


In 


Urine. 


Methane. 


Per Cent. 


Per Cent. 


-1.19 


13.42 


-0.92 


11.12 


-4.95 


- 6.15 


-0.53 


-24.35 


16.59 


0.02 


8.34 


10.78 


4.81 


12.30 


5.62 


19.89 


-0.91 


14.29 



Work of 
Digestion, 
Assimila- 
tion , and 

Tissue 
Building. 
Per Cent. 



43.99 

37.36 

42.77 
41.42 
49.62 



49.08 
52.92 
61.57 
32.09 



In 
Gain. 

Per 
Cent. 



43.88 

52.44 

68.33 
83.46 
33.71 



31.80 
29.97 
12.92 
54.53 



THE UTILIZATION OF ENERGY. 49* 

PERCENTAGE UTILIZATION OF METABOLIZABLE ENERGY. 



Real 

Utilization 

as Computed 

by Kellner. 



Apparent 
Utilization. 



By Ruminants. 

Concentrated Feeding-stuffs : 

Starch, Kiihn's experiments 

" Kellner's expts., moderate rations 
" " " heavy rations... . 

Oil, Sample II, Ox G 

Wheat gluten, Kellner's experiments 

Conglutin, Kern 

Flesh-meal, Kern 



Coarse Fodders : 
Meadow hay. . . . 

Oat straw 

"Wheat straw . . . 
Extracted straw 

By Swine. 

Rice 

Barley 

Mixed grain 



49.0 

58.9 

58.9 

59.4 

45.2* 

67.7* 

65.0* 



41.5 
37.6 
17.8 
63.1 



78.0 
70.9 
68.5 



50.0 
58.4 
61.5 
69.4 
40.3 



41.4 
36.1 
17.4 
63.0 



* Of protein. ; 

The Expenditure of Energy in Digestion, Assimilation, and 
Tissue Building. — As was shown in the introductory paragraphs on 
p. 466, the recorded data do not permit us to distinguish between the 
energy expended in the digestion, resorption, and assimilation of 
the various feeding-stuffs experimented upon and the energy which 
we have reason to believe is required for the conversion of the assim- 
ilated material into tissue. Accordingly these two factors have 
been grouped together in the foregoing summaries of results. Some 
interesting facts are revealed, however, by a comparison of the 
total expenditure of energy for these two purposes in the several 
cases. Kellner's results, as the latest and apparently most accurate 
and representative, have been made the chief basis of the compari- 
son, the figures being those computed by the writer and therefore 
showing the aggregate net effect upon the balance of energy, that is, 
the "apparent" utilization. 

Coarse Fodders. — A comparison of the coarse fodders with 
each other brings out the interesting fact that while the percentage 
of the gross energy recovered in the gain varied from 5.5 to 47.6. 



492 



PRINCIPLES OF ANIMAL NUTRITION. 



the percentage expended in digestion, assimilation, and tissue build- 
ing varied only from 22.85 to 27.98. Expressing the same thing in 
absolute figures, we have the following: 

ENERGY PER GRAM OF ORGANIC MATTER. 





Gross, 
Cals. 


Expended in Diges- 
tion, Assimilation, 
and Tissue Building, 
Cals. 


Meadow hay 

Oat straw 


4.751 
4.816 
4.743 
4.251 


1.327 
1.100 
1.214 
1.190 


Extracted straw 

Average 


4.640 


1.208 



In other words, the combined energy required to separate the 
digestible from the indigestible portion of one gram of organic 
matter, resorb it, and convert the resorbed portion into tissue was 
not greatly different for these four materials. They differed widely 
in their nutritive effect, not because of a greater or less expendi- 
ture of energy for these purposes, but chiefly because the same 
expenditure of energy resulted in making a much larger amount of 
material digestible in some cases than in others. 

Concentrated Feeding-stuffs. — A still more striking result is 
reached when we compare the results on coarse fodders with those 
on concentrated feeding-stuffs. Taking the figures of Kellner's 
experiments for the latter, and omitting his results on heavy 
rations of starch, we have the following data for starch, oil, and 
wheat gluten: 

energy per gram of organic matter. 





Gross, 
Cals. 


Expended in 

Digestion, 

Assimilation, 

and Tissue 

Building, 

Cals. 


Starch (Kellner) 

Oil 

Gluten (Kellner) 


4.168 
9.464 
5.742 


1.277 

1.728 
2.284 



We thus reach the seemingly paradoxical result that the total 
expenditure of energy in the production of new tissue is decidedly 



THE UTILIZATION OF ENERGY. 



493 



greater in the case of these three materials, and notably the last 
two, than in the four coarse fodders previously tabulated. 

The paradox largely disappears, however, when, we remember 
that while the larger share of the work of digestion has to do with 
the total dry matter of the food, the work of assimilation and tissue 
building has to be performed only upon the digested matter, and 
that the proportion of the latter is much larger in the starch, oil, 
and gluten than in the coarse fodders. We have already (pp. 375 
and 445) seen reason to suppose that the processes of assimilation 
and tissue building consume a considerable share of the metaboliz- 
able energy of the food, although we are still ignorant as to how 
much and as to how the proportion differs with different materials, 
and the above results serve to confirm this conclusion. 

If, simply as an illustration, we assume that the uniform pro- 
portion of 30 per cent, of the metabolizable energy of the several 
feeding-stuffs is thus consumed, then if we deduct this amount from 
the totals above computed we shall have the work of digestion alone 
as follows: 

ENERGY PER GRAM OF ORGANIC MATTER. 





Metaboliz- 
able 
Energy 
(p. 297). 
Cals. 


Assumed 
Work of 
Assimilation 
and Tissue 
Building 
(30 Per Cent, 
of Metaboliz- 
able), Cals. 


Total Ex- 
penditure 
as Above. 
Cals. 


Work of 

Digestion Alone 

Cals. 


Meadow hay 

Oat straw 


2.213 
1.724 
1.475 
3.213 
3.079 
5.298 
3.831 


0.664 
0.517 
0.443 
0.964 
0.923 
1.589 
1.149 


1.327 
1.100 
1.214 
1.190 
1.277 
1.728 
2.284 


. 663 1 

583 ! „ „„^ 


Wheat straw 


771 \ - 672 


Extracted straw 


0.192 J 
0.354 
139 


Starch (Kellner) 

Oil 


Wheat gluten (Kellner) . . 


1.1_5 



This arbitrary assumption reduces the work of digestion of the 
starch to about one half that expended upon a like amount of mate- 
rial in the form of coarse fodders which yield chiefly carbohydrates 
to the organism. Moreover, we must remember that in the case of 
starch there is a considerably greater loss of energy in the methane 
fermentation than with the same amount of total organic matter 
in coarse fodders, and that this loss is included in the work of diges- 
tion. The high figure found for the wheat gluten we might be 



494 PRINCIPLES OF ANIMAL NUTRITION. 

inclined to explain by its well-known effect in stimulating the met- 
abolism in the body — that is, by supposing that for this substance 
our assumption of 30 per cent, for the work of assimilation and 
tissue building is too low. 

The computed work of digestion is small in the case of the oil, 
as the results obtained in other experiments would lead us to expect. 
At the same time it should be remembered that the figures given 
are derived from two experiments only, while a third gave quite 
different results, showing in particular a decidedly higher figure for 
the combined work of digestion, assimilation, and tissue building. 
It is obvious, therefore, that further investigation is necessary to 
fix the value of oil in this respect. 

Crude Fiber. — Finally, it will be observed that our arbitrary 
assumption results in making the work of digestion of the extracted 
straw less than two thirds that of starch. We should naturally 
suppose that the mechanical work involved in digestion would be 
fully as great in the case of the former as in that of the latter, while, 
as the figures for methane show, the extracted straw underwent a 
more extensive fermentation than the starch. Obviously, the 
mechanical and chemical treatment to which the straw was sub- 
jected so modified the cellulose and removed incrusting matters as 
to produce a material which behaved substantially like starch in the 
alimentary canal, both as regards its digestibility and its relation to 
ferments* Correspondingly, the total work of digestion, assimila- 
tion, and tissue building is not widely different in the two cases. It 
is only when we arbitrarily assume a high percentage for the work of 
assimilation and tissue building, as was done above for the sake of 
illustrating the general question, that this difference and that in the 
amount of metabolizable energy combine to give the relatively low 
figure for digestive work noted above. 

§ 2. Utilization for Muscular Work. 

When a muscle is subjected to a suitable stimulus (normally a 
nerve stimulus) there occurs, as we have seen, a sudden and rapid 
increase in its metabolism. This increased metabolism appears to 

* Lehmann (Landw. Jahrb., 24, Supp. I, 118) had previously shown that 
the apparent digestibility of the crude fiber and nitrogen-free extract of straw 
and chaff thus treated was increased by from 79 to 133 per cent. 



THE UTILIZATION OF ENERGY. 495 

consist largely in a breaking down or cleavage of some substance or 
substances contained in the muscle, resulting in a rapid increase in 
the excretion of carbon dioxide and the consumption of oxygen by 
the animal. In this process of breaking down or cleavage there is a 
corresponding transformation of energy, a portion of the potential 
energy of the metabolized material appearing finally as heat, while 
a part may take the form of mechanical energy. The inquiry 
naturally arises what proportion of the total energy liberated during 
the increased metabolism is recovered as mechanical work and what 
proportion takes the form of the (for this purpose) waste energy of 
heat. The question is not only one of great theoretical interest to 
the physiologist, but the efficiency of the working animal regarded 
as a machine for the conversion of the potential energy of feeding- 
stuffs into mechanical work is also of the highest practical im- 
portance. 

Efficiency of Single Muscle. — A large amount of experi- 
mental work has been devoted to the study of the single muscle as a 
machine. The subject is a complicated one, and unanimity of views 
upon it has by no means been attained, especially as to the mechan- 
ism of muscular contraction. As regards the efficiency of the muscle 
as a converter of energy, however, one fact is perfectly well estab- 
lished, viz., that it varies within quite wide limits. 

If the two ends of a muscle be attached to fixed points, so that 
it cannot shorten, a suitable stimulus will still cause it to contract 
in the technical sense of the word; that is, a state of tension will 
be set up in the muscle tending to pull the two supports nearer 
together (isometric contraction). In such a contraction there is 
an expenditure of potential energy and a corresponding increase 
of muscular metabolism, but no external work is done. In other 
words, all the potential energy finally takes the form of heat and 
the mechanical efficiency is zero. This is the case, for example in 
the standing animal. A not inconsiderable muscular effort is 
required to maintain the members of the body in certain fixed 
positions, and a corresponding generation of heat takes place, but 
no mechanical work is done. 

But even when the muscle is free to shorten and thus do mechan- 
ical work, its efficiency is found to be variable, the chief determin- 
ing factors being the load and the degree of contraction. The 



49 6 PRINCIPLES OF ANIMAL NUTRITION. 

maximum efficiency of the muscle is reached when the load is such 
that the muscle can just raise it, while this maximum load dimin- 
ishes as the 'muscle contracts until when the latter reaches the limit 
of shortening it of course becomes zero. Conversely, if the muscle 
be stretched beyond what may be called its normal length, as is 
the case in the living body, the weight which it can lift, and conse- 
quently its efficiency, is increased. In these respects the muscle 
behaves like an elastic cord, and some authorities, notably Chau- 
veau,* regard the essence of muscular contraction as consisting of 
a direct conversion of the potential energy of the "contractile 
material " of the muscle into muscular elasticity. 

Efficiency of the Living Animal. — According to the above 
principles the maximum efficiency of a muscle would be obtained 
when it was loaded to its maximum at each point in the contraction ; 
that is, when the load diminished uniformly from the maximum 
corresponding to the initial length of the muscle to zero at the point 
of greatest contraction. Such conditions, however, rarely if ever 
obtain in the animal. Of its many muscles some serve largely 
or wholly to maintain the relative positions of the different parts of 
the body, and consequently have an efficiency approaching zero. 
Others contract to a varying extent and under loads less than the 
maximum. Some muscles, owing to their anatomical relations, 
work at a less mechanical advantage than others, while the extent 
to which a given group of muscles is called into action will vary 
with the nature of the work. 

If, then, the efficiency of the single muscle is variable, that of 
the body as a whole would seem likely to be even more so, thus 
rendering it difficult to draw any trustworthy direct conclusions 
as to the efficiency of the bodily machine from studies of the effi- 
ciency of the single muscle. Moreover, the performance of labor 
by an animal sets up various secondary activities, notably of the 
circulatory and respiratory organs, which consume their share of 
potential energy and yet do not contribute directly to the per- 
formance of the work, and the extent of these secondary activities 
varies with the nature and the severity of the work. When, there- 
fore, as is here the case, we consider the whole animal in the light 
of a machine for converting the potential energy of the food into 
* Le Travail Musculaire. Paris, 1891. 



THE UTILIZATION OF ENERGY. 497 

mechanical work, we are perforce, by the very complexity of the 
problem, driven to the statistical method of comparing the total 
income and outgo of energy in the various forms of work. 



THE UTILIZATION OF NET AVAILABLE ENERGY. 

Both the activity of the skeletal muscles in the performance of 
work and the supplementary activity of the muscles concerned in 
circulation, respiration, etc., is carried on at the expense of energy 
stored in the muscles themselves or perhaps in the blood which 
circulates through them. The body thus suffers a loss of energy 
which is replaced from the energy of the food. If, then, we supply 
a working animal, in addition to its maintenance ration, with an 
amount of food exactly sufficient to make good the loss, the total 
energy metabolized in the performance of the work will repre- 
sent the net available energy of the excess food, since this by 
definition is that portion of the gross energy which contributes 
to the maintenance of the store of potential energy in the 
body. 

It is true that in our discussion of the net available energy of 
the food we regarded it as making good the losses that occur below 
the maintenance requirement, and the question may arise whether 
the availability as thus measured is the same as the availability for 
the production of muscular work. In reality, however, the two 
cases are not radically different. Even below the point of mainte- 
nance the internal work of the body consists very largely of muscu- 
lar work, and it is the energy metabolized in the performance of this 
work which appears to constitute the chief demand for available 
food energy. It would appear highly probable, therefore, that the 
net availability of the metabolizable energy of the food will be found 
to be substantially the same whether that energy be employed to 
prevent a loss from the body as a consequence of its internal work 
below maintenance or on account of the performance of external 
work above maintenance. 

If, then, we cause an animal to perform a known amount of 
external work and measure the increase in the amount of energy 
metabolized in the body, we may regard the latter as representing 
net available energy derived from previous food, and a comparison 



49 8 PRINCIPLES OF ANIMAL NUTRITION. 

of this quantity with the work done will give the coefficient 
of utilization for the particular animal and kind of work experi- 
mented on. 

The Efficiency of the Animal as a Motor. 

The relation just indicated between the work performed and the 
total energy metabolized in its performance is not infrequently re- 
garded as expressing the efficiency of the animal as a motor, but it- 
should be clearly understood that this is true only in a limited sense. 
A coefficient computed in the manner outlined above takes account 
only of the loss which occurs in the conversion of the stored energy 
of the body into external mechanical work. It neither includes the 
expenditure of energy required for the digestion and assimilation of 
the food, nor does it take account of the large amount of energy con- 
tinually consumed in the internal work of the animal machine. It 
does not, therefore, furnish a direct measure of the economy with 
which the animal machine uses the energy supplied to it, but is 
comparable rather to the theoretical thermo-dynamic efficiency of 
a steam-engine. With this limitation, however, the phrase maybe 
used as a matter of convenience. 

Quite extensive investigations upon this point are already on 
record. They have generally taken the form of what may be called 
respiration experiments. The respiratory exchange of carbon di- 
oxide and oxygen has been determined, first, in a state of rest, and, 
second, during the performance of a measured amount of work. 
From the difference between these two values the quantity of ma- 
terial metabolized and the amount of energy consequently liberated 
have been computed and compared with the energy recovered in 
the form of mechanical work. 

This method of experimentation has been largely developed and 
employed by Zuntz and his associates * in experiments upon man, 
the dog, and especially the horse. Since the present work relates 
especially to the nutrition of domestic animals, the results upon the 
latter animal are of peculiar interest, but their study may be ad- 
vantageously preceded by a somewhat brief consideration of the 
results upon the dog and upon man. 

* Compare Chapter VIII, pp. 251-2 



THE UTILIZATION OF ENERGY. 



499 



Experiments on the Dog. — The following experiments by 
Zuntz,* while not the earliest upon record, may serve to illustrate 
the general methods employed and as introductory to the more 
elaborate experiments upon the horse. 

The following table shows the average oxygen consumption and 
carbon dioxide excretion, determined by the Zuntz apparatus, of 
a dog when lying, standing, and performing work upon a tread- 
power, and also the amount of work done, all computed per minute : 



Weight 




of Ani- 


No of 


mal 


Ex- 


and 


peri- 


Load 


ments. 


Kgs. 






6 




2 


26 . 932 


8 


26 . 674 


5 


27.175 


10 



Lying 

" (Magnus-Levy) . . 

Standing 

Ascending slight incline. 

steeper ' 
Draft nearly horizontal . 



Respiration per 
Minute. 



Oxy- 
gen 
c.c. 



174.3 
172. 
245.6 
725.3 

1285.3 
1028.8 



OO2 
c.c. 



124.7 
123.8 
170.2 
525.2 
990.6 
798.9 



Respir- 
atory 
Quo- 
tient. 



0.71 
0.72 
0.69 
0.73 
0.77 
0.77 



Work per Minute. 



Work Work 

of J of 
Ascent j Draft. 
Kgm. Kgm. 



13.23 

365.82 

22.83 



202.91 



Dis- 
tance 
travel- 
led. 
Meters. 



78 . 566 
79.497 
70.420 



The work per minute as given in the above table does not in- 
clude the energy expended in horizontal locomotion. The work of 
draft is the product of the distance traversed into the draft; the 
work of ascent equals the same distance multiplied by the sine of 
the angle of ascent. A remarkable increase (41 per cent.) in the 
metabolism when standing over that when lying was observed 
(compare p. 343) but does not enter into the subsequent com- 
putations. 

The two experiments on ascending a grade afford data for com- 
puting the increased metabolism corresponding, on the one hand, 
to one gram-meter of work done against gravity, and, on the 
other, to the transportation of tme kilogram through one meter 
horizontally. The latter, of course, is not work in the mechanical 
sense, but it requires the consumption of a certain amount of 
material, the liberated energy being employed in successive liftings 
of the body and in overcoming internal resistances and ultimately 
appearing as heat. It includes, of course, the increased metab- 
olism required for the maintenance of the erect position. 



* Arch. ges. Physiol., 68, 191. 



5°° 



PRINCIPLES OF ANIMAL NUTRITION. 



If from the totals given in the table we subtract the figures 
for rest, we have the following as the increments of the respiration 
due to the work, including the work of standing : 





Oxygen, 
c.c. 


Carbon Dioxide, 
c.c. 


Ascending slight incline . . 
" steeper " 

. 


551.0 
1111.0 


,00.5 
865.9 



The weight of the animal and the distance traversed having 
differed somewhat, the results may be rendered comparable by com- 
puting them per kilogram of weight and per meter of distance trav- 
ersed — that is, by dividing in each case by the product of weight 
into distance. Expressing the results in gram-meters and cubic 
millimeters for convenience we have — 



Oxygen 
c.mm 



Carbon Dioxide 
c mm. 



Work of Ascent, 
gr.-m. 



Ascending slight incline . . . 
" steeper " 



260.40 
523.93 



189.27 
408 . 35 



6.252 
172.512 



If we let x equal the oxygen consumption required for the trans- 
portation of 1 kg. through 1 meter and y that required per gram- 
meter of work of ascent we have 



x + 6. 252?/ = 260. 40 c.mm. 
x + 172. 512?/ = 523. 93 c.mm. 



whence we have 



2 = 250.49 c.mm. 
y = 1.585 c.mm. 

A similar computation for the carbon dioxide gives 

Locomotion, per kg. and meter 181 . 033 c.mm. 

Per gram-meter of work of ascent .... 1.317 c.mm. 

and the corresponding respiratory quotient is 0.723. 

With these data in hand it is easy to compute the increased 
respiratory exchange corresponding to one gram-meter of work of 
draft as follows: 



THE UTILIZATION OF ENERGY. 



5°i 





Oxygen, 

C.C. 


Carbon Dioxide, 

C.C. 


Total 


1028.80 
174.30 

479.36 
36.19 


124 . 70 

346.55 
30.07 


798 90 


Rest 




Transportation of 27.175 kgs. 

through 70.42 meters 

Ascent — 22.83 kgm 








Total 


689.85 




501.32 




Remains for draft 


338.95 


297.58 





For one gram-meter of work of draft we have, therefore, 

Oxygen 1 . 6704 c.mm 

Carbon dioxide 1 . 467 c.mm 

Respiratory quotient 0.878 

It appears from the above that the work of draft required 
somewhat more metabolism than the same amount of work of 
ascent. The individual experiments of this and other series like- 
wise show that variations in the speed and in the angle of ascent 
affect the result. For the present, however, we may confine our- 
selves to a consideration of the average figures. 

It remains to compute from the results for oxygen and carbon 
dioxide the corresponding amounts of energy liberated. The data 
are insufficient for an exact computation. It having been shown, 
however (compare Chapter VI), that even severe work causes but a 
slight increase in the proteid metabolism, the author assumes that 
the additional metabolism in these experiments was entirely at the 
expense of carbohydrates and fat and computes the proportion of 
each from the respiratory quotient. The results are admittedly 
not exact. Besides the uncertainty just mentioned, there is the 
possibility that irregularities in the excretion of carbon dioxide 
may affect the respiratory quotient in short trials and, more- 
over, we must bear in mind the possibility of various cleavages 
and hydrations as affecting the evolution of energy in such experi- 
ments (compare Berthelot's criticism on p. 254). The author does 
not, however, regard these possible errors as very serious. Com- 
puted on this basis the results are as follows, expressed both in 
terms of heat (calories) and in gram-meters (1 cal. equals 425 
gram-meters) : 



502 PRINCIPLES OF ANIMAL NUTRITION. 

For 1 gram-meter, ascent . 0076681 cal. = 3 . 259 gr.-m. 

" 1 " " draft 0.008180 " =3.476 " 

" locomotion per kg. and meter . . 1.1787 cals. = 500.95 " 

According to the above figures the performance of one gram- 
meter of work required the metabolizing of material whose potential 
energy was equal to 3.259 gr.-m. in the one case and 3.476 gr.-m. in 
the other. In other words, these amounts of net available energy 
were liberated in the kinetic form in the body, one gram-meter in 
each case being recovered as external work while the remainder 
ultimately took the form of heat. 

This is equivalent to a utilization of 30.7 per cent, of the net 
available energy in ascent and of 28.77 per cent, in draft. It is to 
be noted that these figures refer only to that portion of the in- 
creased metabolism which is applied to the production of external 
work and do not include that necessary for the transportation of the 
animal's weight. The corresponding ratio for this portion could 
only be obtained on the basis of complicated and uncertain compu- 
tations of the mechanical work of locomotion. If, however, instead 
of this we assume that this most common form of muscular activity 
is performed with the same economy as the work of ascent, we can 
conversely compute the mechanical work of locomotion for 1 kg. 
through 1 meter as 

500 . 95 gr.-m. X . 307 = 153 . 8 gr.-m. 

Experiments on Man. — In connection with his experiments on 
the dog already described, Zuntz * cites the results of a number of 
experiments with man upon the work of locomotion and of ascent, 
the average results of which are summarized in the table opposite, 
to which have been added the results of later experiments by 
Frentzel & Reach. f 

Experiments on the Horse. — Very extensive investigations on 
the production of work by the horse have been made by Zuntz in 
conjunction with Lehmann and Hagemann.J Some of the results 
of these investigations have already been discussed in their bearing 
on the question of digestive work (pp. 385-393), and the method 

* Lor cit., p. 208. 

t Arch, ges Physiol.. 83, 494. 

X Landw. Jahr.", 18, 1; 23, 125; 27, Supp III. 



THE UTILIZATION OF ENERGY. 



5°3 





Weight 
(with 

Appara- 
tus), 
Kgs. 


Energy Expended in 


Horizontal 
Velocity 

per 
Minute, 
Meters. 




Experimenter. 


Loco- 
motion 
per Kg. 
and Meter, 
Kgm. 


Per Kgm. 

Work of 

Ascent, 

Kgm. 


Grade, 
Per Cent. 


Katzenstein 


55.5 
72.9 
67.9 
80.0 

88.2 
72.6 
81.1 
80.0 

86.5 
86.5 

65.8 
55.8 


0.334 

0.217 
0.211 
0.288 
0.263 
0.284 
0.231 
0.244 

0.219 
0.233 

0.230 
0.251 


2.857 
3.190 
3.140 
3.563 
3.555 
2.913 
2.921 
2.729 

[2.746 | 
I 2.846 j 


74.48 
71.32 ) 
71.46 J 
51.23 | 
43.34 f 
62.04 ) 
60.90 [ 
56.54 ) 

66.94] 
3, .92 1 

Y 
63.95 | 
34.58 J 


9 6 13 3 


r 

1 

Schumburg & Zuntz ■{ 

1 
I 

Loewy -| 

Frentzel : 

Normal gait 


6.5 
30.7-62.0 

23.0-30.5 


Slow " 




Reach : 

Normal gait 

Slow " 


23.3 







of computing the total metabolism in the rest experiments has 
been explained; it remains to consider the results of the work 
experiments. The larger proportion of the experiments were 
upon the same horse (No. Ill), and the summaries and averages 
on subsequent pages represent chiefly the results with this animal. 

The work was done upon a special tread-power located in the 
open air, and during the rest experiments the animal likewise stood 
in the tread-power. The inclination of the platform of the power 
could be varied, and it could also be driven by a steam-engine, so 
that by setting it horizontal the work performed by the animal was 
reduced to that of locomotion alone. The distance traversed was 
measured by a revolution-counter, and in the experiments on draft 
the animal pulled against a dynamometer. 

The large number of experiments (several hundred) are grouped 
by the authors into fourteen periods according to the season (winter 
or summer) and the kind and amount of food consumed, each of 
these periods including a considerable number of experiments both 
on rest and on different forms of work. On each day from two to 
eight experiments were usually made, some on rest and some on 
work of various sorts. The average of all the rest experiments in 
each period is then compared with similar averages for the various 



5°4 



PRINCIPLES OF ANIMAL NUTRITION. 



kinds of work in order to eliminate so far as possible the influence 
of variations in external temperature and in the feeding, as well as 
to reduce the probable error of experiment. 

Work at a Walk. — The experiments may be grouped into 
those in which the work was performed respectively at a walk and a 
trot. Those of the former category, being the more numerous, may 
be considered first. 

Work of Locomotion. — The following detailed comparison of the 
experiments of Period a upon rest and upon walking without load 
or draft will serve to further explain the method : 



REST EXPERIMENTS. PERIOD a. 
Ration, 6 Kg. Oats, 1 Kg. Straw, 6-7 Kg Hay. 



No. of Experiment. 


Per Kg Live Weight 
and Minute. 


Respira- 
tory 
Quotient. 


Air Tem- 
perature 
Deg. C. 


Relative 
Velocity 
of Wind. 


Hours 
Since Last 
Feeding. 


Oxygen 
c.c. 


Carbon 

Dioxide 

c.c. 


37a 


3.94 
3.92 
3 98 
4.06 
4.11 
3.89 
3 71 


3.81 
4 02 
3.42 
4.04 
3 86 
3.63 
3.44 


0.968 
1.025 
0.861 
0.997 
0.940 
0.933 
0.929 


-5.0 
-0.5 
2.0 
5.3 
4.7 
2.0 
9.0. 



1 
1 
3 
1 
1 
3 


3.0 


38& 


2.5 


38/ 


5.6 


39a 


2.0 


44a 


1.5 


45g 


3.5 


46a 


1.5 






Average 

Corrected *..... 


3.94 
4.04 


3.75 
3.86 


0.950 


2.5 


1.4 


2.8 



In the same period eight experiments were made in which the 

^ad-power was set as nearly horizontal as possible and driven by 

the steam-engine, the animal being simply required to maintain his 

place on the power. The results for oxygen were as shown in the 

first portion of the following table : 

* A comparison of Zuntz's method with the results obtained in the Pet- 
tenkofer respiration apparatus showed that the gaseous exchange through 
the skin and intestines amounted to about 2\ per cent, of the pulmonary 
respiration in case of the oxygen and 3 per cent in case of the carbon di- 
oxide. These additions are accordingly made to the figures of the respira- 
tion experiments and the results designated as "corrected." 



THE UTILIZATION OF ENERGY. 



5°5 



WALKING WITHOUT LOAD OR DRAFT. 
Per Kg. Live Weight. 



PERIOD a. 





Live 

Weight 

Kgs. 


Observed. 


Oxygen Equivalent 


No. of 
Experiment. 


Per Minute. 


Work of 

Ascent, 

Per Meter 

Traveled. 

Gr.-m. 


to Work. 


Oxygen 
c.c. 


Distance 

Traveled 

Meters. 


Work of 

Ascent, 

Kgm. 


Per 

Minute, 
c.c. 


Per Meter 

Traveled. 

c.mm. 


40d 


429 
434 
428 
428 
430 
430 
434 
434 


9.0 
11.3 
12.2 
12.7 
10.8 
11.7 
12.3 
11.2 


57 

87 
94 
95 
92 
99 
98 
93 


0.57 

0.84 
0.89 
0.87 
0.70 
0.74 
0.79 
0.76 


10 
10 

9 
9 

8 
8 
8 
8 


5.1 

7.3 

8.2 
8.7 
6.9 
7.8 
8.4 
7.3 


89 


446 


84 


456 


88 


45d 


92 


466 


74 


46c 


79 


476 

47c 


86 

78 


Average .. . 
Corrected. . 


430.9 


11.405 


89.338 


0.764 


8.643 


7.463 


83.793 

85 888 



















If from the oxygen consumption in each of the above experiments 
we subtract the average rest value for the same period (3.94 c.c.) 
the remainder will represent the increase due to the work, as shown 
in the seventh column, and this divided by the distance traveled 
gives the figures of the eighth column. 

The average respiratory quotient of that part of the respiration 
due to the work in these eight experiments was 0.894. On the 
very probable assumption that the work caused no material change 
in the metabolism of either proteids-* or crude fiber, or in other 
words, that the energy for work was derived substantially from solu- 
ble carbohydrates and fat, the calorific equivalent of 1 c.c. of oxygen 
is computed and the following calculation of energy made for the 
average of the eight experiments (compare pp. 76 and 251). These 
results are not corrected for cutaneous and intestinal respiration. 
Per Kg. Live Weight per Minute. 

Oxygen combined with fat 3.4415 c.c. 

Oxygen combined with starch 4.0215 " 



Total 7.4630 " 

Equivalent energy 36 . 420 cals. 

* The authors show that even a considerably increased proteid meta- 
bolism would not materially affect the computation of energy. 



506 



PRINCIPLES OF ANIMAL NUTRITION. 



Energy per Meter Traveled (Including Work of Ascent). 
Per kg. total mass * 0.3948 cal. 

p l r ■ i* (0.4077 " 

Per kg. live weight j Q 1733 kgm 

Work of ascent 8 . 643 gr.-m. 

Determinations of the work of locomotion were made in six 
different periods, or thirty-five experiments in all. The average 
for each period, computed in terms of energy as in the above 
example, is given in Table VIII of the Appendix. It is to be noted 
that these results still include the small amount of work expended 
in ascending the slight incline. This factor is determined in the 
manner shown in the following paragraph. 

Work of Ascent. — In four periods experiments were made (thir- 
teen in all) upon the work of ascending a moderate grade at a walk. 
The average results, computed on the same basis as before, are 
contained in Table IX of the Appendix. 

By comparing the average results of these two series of experi- 
ments in the manner explained on p. 500, letting x equal the oxygen 
or energy required per kilogram live weight for locomotion through 
1 meter horizontally and y the corresponding quantities for the 
performance of 1 gram-meter of work of ascent we have the follow- 
ing equations: 

For Oxygen. 
x+ 4.395?/= 83.480 c.mm. 
x+ 107.04k/ = 222. 941 c.mm. 

For Energy. 
x+ 4. 395?/ = 0.4035 cal. 
z+107.041?/=1.0795cals. 
Solving these we obtain the following values respectively for 
the work of locomotion per meter and for the energy expended in 





Oxygen, 
c mm. 


Energy. 




cals. 


Kgm. 


Locomotion per meter: 

Per kg. live weight 

Ascent, per kilogram-meter 


77.509 
75 . 048 
1359.00 


0.3746 
0.3618 
6.5858 


0.1592 
0.1538 
2 . 7990 



* Weight of animal plus weight of apparatus carried. 



THE UTILIZATION OF ENERGY. 



5°7 



doing 1 kgm. of work of ascent, and the utilization of the available 
energy in the latter case is 35.73 per cent. 

Work of Draft. — For the work of draft at a walk, up a slight 
incline, the results tabulated in Table X of the Appendix were 
obtained. 

Giving x and y the same significance as before, and letting z 
represent the oxygen or energy corresponding to one gram-meter of 
vvork of draft, we have the following equation, based on the results 
per kilogram live weight and meter traveled: 

£ + 5.115?/+ 153. 127z = 306. 561 c.mm. = 1.5021 cals. 

Substituting in this the average values of x and y obtained as in- 
dicated in the previous paragraph, but from a larger number of 
experiments, we have 

z = 1 .4504 c.mm.= .007143 cal. per gram-meter. 

The above details of a few of the experiments may serve to illus- 
trate the methods of computation employed. Similar determina- 
tions were made upon various forms of work under differing condi- 
tions, the results of which will be given later. 

Correction for Speed. — Before final data could be obtained, 
however, it was found necessary to take account of the speed of the 
animal, since comparisons of the various periods showed that the 
metabolism due to the work of locomotion at a walk increased 
materially as the velocity increased. 

To compute the necessary correction, the authors divide the 
thirty-five experiments of Table VIII into three groups according 
to the speed. For each group the oxygen and energy correspond- 
ing to the work of ascent are computed, using the values of y given 
on the previous page (1359 c.mm.; 6.5858 cals.), and subtracted 
from the total, leaving the following as the amounts per kilogram 
live weight due to horizontal locomotion: 



No. of 
Experi- 
ments. 


Velocity 

per Minute, 

Meters. 


Oxygen 
Consumed 

per Kg. 
and Meter, 

c.mm. 


Respira- 
tory 
Quotient. 


Oxygen Re- 
calculated to 
Respiratory 
Quotient of 
0.86, c.mm 


Increase of 
Oxygen per 

Meter 
Velocity, 

c.mm. 


Heat Value 
of Oxygen 
per Meter 

(Corrected), 
cals. 


6 

20 

9 


78.00 
90.16 
98.11 


66.69 
76.04 
80.97 


0.896 
0.848 
0.873 


67.32 
75.80 
81.23 


0.697 
0.683 


0.3363 
0.3787 
0.4058 









5 o8 



PRINCIPLES OF ANIMAL NUTRITION. 



On the average, an increase of 1 meter per minute in the speed 
was found to cause an increased metabolism corresponding to — 

Oxygen . 692 c.mm. 

Energy 0.00345 cal. 

A similar computation for the experiments on ascending a con- 
siderable grade without load or draft showed a similar difference, 
which, however, seemed to be chiefly or entirely due to variations 
in the work of locomotion. When the amount of the latter was 
computed with the correction for speed just given, the metabolism 
due to the actual work of ascent seemed to be independent of the 
speed, the only exception being two experiments at a rapid walk in 
which over exertion of the animal was suspected. 

In the thirteen experiments on the work of ascending a moderate 
grade contained in Table IX, the average speed was 81.95 meters 
per minute, while in the thirty-five experiments with which they 
are compared (Table VIII) the average speed was 90.16 meters. 
From the table on p. 506 we compute that the consumption of 
oxygen (R.Q. = 0.86) and the corresponding energy values per kilo- 
gram and meter at these speeds would be — 





Oxygen, 
c.mm. 


Energy, 
cals. 


At 90.16 M. velocity 

" 81.95 M. " 


75.80 
70.05 


0.3746 
. 3462 



Substituting this corrected value of x in the equations on 
p. 506, we have as the corrected value of y per kilogram-meter for 
ascending a moderate grade 

6 . 851 cals. = 2.912 kgm. = 34 . 3 per cent. 

In brief, a correction for the value of x is computed, using the 
first value of y, and then this corrected value of x is used to com- 
pute the corrected value of y. In other words, the method is one 
of approximation, but the errors of the corrected values are pre- 
sumably less than the unavoidable errors of experiment. 

Effect of Load. — In a number of experiments the horse carried 
on the saddle a load, consisting of lead plates, corresponding to that 
of a rider. The mere sustaining of such a weight at rest was found 



THE UTILIZATION OF ENERGY. 509 

to increase the gaseous exchange, the total metabolism being sub- 
stantially proportional to the total mass (horse + load), but in com- 
puting the work experiments the same rest values are used as for 
the preceding experiments; that is, the results include the work 
required to simply sustain the weight as well as that required to 
move it. Computing the results in the same manner as before the 
authors obtain for an average speed of 90.18 meters per minute 
the following results: 

Locomotion per Meter. 

Per kg. live weight 0.5004 cal. = 0.2126 kgm. 

" " total mass 0.3914 " =0.1663 " 

Ascent. 

Per kilogram-meter 6.502 cals. = 2.7640 " = 36. 19# 

A comparison of these figures with those on p. 506 shows 
that for this animal a load of 127 kgs. caused about 8 per cent, 
increase in the energy expended, per kg. of total mass, in horizon- 
tal locomotion, but no increase in that expended per kilogram- 
meter in ascent. 

Work of Descent. — In descending a grade the force of gravity 
acts with instead of against the animal and tends therefore to 
diminish the metabolism. On the other hand, however, as the 
steepness of the grade increases the animal is obliged to put forth 
muscular exertions to prevent too rapid a descent, and this tends 
to increase the metabolism. It was found that an inclination of 
2° 52' caused the maximum decrease in the metabolism. At 5° 45' 
the metabolism was the same as at 0°, while on steeper grades it 
was greater than on a level surface. 

Work at a Trot. — A smaller number of experiments were made 
upon work at a trot under varying conditions. In trotting, the up 
and down motion of the body is much greater than in walking, while 
but a small part of the muscular energy thus expended is available 
for propulsion. It was therefore to be expected that the energy 
required for horizontal locomotion would be greater at a trot than 
at a walk, and the results of the experiments corresponded fully 
with this expectation, the computed energy per meter being found 
to be 

Per kg. live weight 0.5660 cal. 

mass (horse + load) 0.5478 " 



U (I 



5i° 



PRINCIPLES OF ANIMAL NUTRITION. 



at a speed of 195 meters per minute. The fact of such an increased 
expenditure of energy in trotting as compared with walking has 
also been confirmed by the results of Grandeau, which will be con- 
sidered in another connection. It was also found that in trotting, 
unlike walking, the work of locomotion was independent of the 
speed within the limits experimented upon (up to a speed of 206 
meters per minute, or about 1\ miles per hour) . A load of 127.2 kgs. 
increased the work of locomotion per kg. of mass by about 10 per 
cent, as compared with the increase of 8 per cent, at a walk. One 
experiment on work of ascent and one on horizontal draft, both 
without load, showed a utilization of , respectively, 31.96 percent, 
and 31.70 per cent., but two other experiments on horizontal draft, 
in which the work was thought to have been excessive, gave an 
average of only 23.35 per cent. 

Summary. — The final results of the experiments upon the horse 
may be summarized as follows: 



Work at a Walk. 



Available Energy utili 



For 1 kgm. work of ascent, 
without load : 

10.1% grade 

18.1$ grade 

For 1 kgm. work of ascent, 
with load : 

15.8$ grade 

For 1 kgm. work of draft : 



0.5 % grade 



8.5 % grade 

Locomotion per kg mass per 
meter without load : 
Speed of 78 00 M. permin 
" " 90.16 " " " 
" " 98.11 '• " " 
The same with load : 

Speed of 90.18 M per min 



Expended 



cals. 



8508 
9787 



502 



5190 



Kgm. 



2.9116 
2 . 9660 



2 . 7634 



3.1960 



10.3360 4.3930 



3256 
3666 
3929 



0.3914 



tion 

Per 

Cent. 



34.3 
33.7 



36.2 

31.3 
22.7 



Work at a Slow Trot 



Available Energy 
Expended. 



cals. 



7.3647* 



7.4240* 
10.0780t 



0.5478} 
0.6007} 



Kgm 



Utiliza- 
tion. 
Per 
Cent 



3 . 1300* 



3.1550* 

4.2820f 



31.96* 



31.7* 

23. 4f 



* Single experiment. 

■j Two experiments. Work probably excessive. 

% Independent of speed. 



THE UTILIZATION OF ENERGY. 5 11 

Conditions Determining Efficiency. 

From the results recorded in the preceding paragraphs it appears 
that, as we were led to expect from a consideration of the efficiency 
of the single muscle, the efficiency of the animal as a converter of 
potential energy into mechanical work varies with the nature of the 
work and the conditions under which it is performed, although the 
variations are perhaps hardly as great as might have been expected. 
In general, we may say that in the neighborhood of one third of the 
potential energy directly consumed in muscular exertion is recov- 
ered as mechanical work. This appears to be a high degree of effi- 
ciency as compared with that of any artificial transformer of poten- 
tial energy yet constructed. The steam-engine, the chief example 
of such transformers, even in its most highly perfected forms, rarely 
utilizes over 15 per cent, of the potential energy of the fuel, while 
in ordinary practice one half of this efficiency is considered a good 
result. 

The comparison is misleading, however, for three reasons : First, 
the figures given in the preceding pages relate to the utilization of 
the net available energy of the food. As we have seen, however, 
a certain expenditure of energy in digestion and assimilation is 
required to render the food energy available, while still another 
portion of the latter is lost in the potential energy of the excreta. 
In the case of herbivorous animals, these two sources of loss very 
materially reduce the percentage utilization when computed upon 
the gross energy of the food. Second, the comparison takes no 
account of the large amount of energy consumed continually 
throughout the twenty-four hours for the internal work of the 
body of the animal, and which continues irrespective of whether 
the animal is used as a motor or not. Third, the expenditure 
of energy in locomotion is not considered in computing the 
efficiency of one third. When these three points are allowed for 
but little remains of the apparent superiority of the animal as a 
prime motor, even omitting from consideration the greater cost of 
his fuel (food). 

It remains now to consider somewhat more specifically the in- 
fluence upon the efficiency of the animal machine of some of the 
more important conditions. 



5i2 



PRINCIPLES OF ANIMAL NUTRITION. 



Kind of Work. — Of the forms of work investigated, that of 
ascent, that is, of raising the weight of the body (with or without 
load), appears to be the one which is performed most economically. 
The horse in ascending a moderate grade without load showed an 
efficiency of 34.3 per cent., while with a load of 127 kgs. a slightly 
higher efficiency was obtained, viz., 36.2 per cent. (The latter 
figure, however, includes some estimated corrections for speed.) 
For the dog (p. 502) the average result was 30.7 per cent. For 
man the figures of the table on p. 503 correspond to from 28.1 to 
36.6 per cent. 

The efficiency, however, was found to decrease with the steep- 
ness of the grade. Thus with the horse it fell from 34.3 to 33.7 
per cent., with an increase of the grade from 10.7 to 18.1 per cent. 
The experiments of Loewy on man, averaged on p. 503, show the 
same result in a more striking manner. Taking separately the 
experiments on each subject we have the following: 



Grade 
Per Cent. 


Efficiency. 


A, L. 
Per Cent. 


J. L 
Per Cent. 


L Z 

Per Cent. 


23 

30.5 

36.6 


34 3 
34 3 
29.0 


36.1 
32.6 
32 3 


36.6 

36 6 
32.2 



The work of horizontal locomotion consists largely of successive 
liftings of the weight of the body. It might therefore be expected 
from the above results that this work would be performed even more 
economically than that of ascent, since it is obviously the form of 
muscular activity for which animals like the horse and dog arc 
specially adapted. In the case of the walking horse, Kellner * has 
proposed a formula based on mechanical considerations, for com- 
puting the work of locomotion. Zuntz f has applied this formula 
to the animal used in his experiments and computed the mechanical 
work of locomotion at the three speeds for which the total metabo- 
lism was also determined (p. 507). 

Landw. Jahrb., 9 658. 
t/&id, 27. Supp TIL. p 314. 



THE UTILIZATION OF ENERGY. 



513 



A comparison of these figures, expressing the total metabolism 
in its mechanical equivalent, is as follows: 



Speed 

Meters per 

Minute. 


Per Kg. Mass and Meter. 


Total Computed 
Metabolism Work 
Gram-meters. | Gram-meters. 


Percentage 
Efficiency. 


78.00 
90.16 
98.11 


138.4 
155.8 
167.0 


49.14 
54.54 

58.40 


35.5 

35.00 

34.97 



This computation gives an efficiency slightly greater than that 
obtained for the ascent of a grade without load, and in so far tends 
to confirm our conjecture, but the basis on which the work of loco- 
motion is computed can hardly be regarded as sufficiently accurate 
to give this result the force of a demonstration. 

The work of draft appears to be performed considerably less 
economically than that of ascent or locomotion. Thus, for the 
horse, the efficiency for nearly horizontal draft was found to be 31.3 
per cent, at a walk, and in one experiment at a trot 31.7 per cent., as 
against 34-36 per cent, for ascent. In two other experiments at a 
trot, in which the work may have been excessive, a much lower 
efficiency was found, viz., 23.4 per cent. For draft up a grade of 
8.5 per cent, at a walk the efficiency was greatly reduced, viz., to 
22.7 per cent. The above figures refer to the work of draft only, 
after deducting the energy required for locomotion and ascent. A 
similar difference was likewise observed with the dog (p. 502), the 
efficiency in nearly horizontal draft being 28.8 per cent, as compared 
with 30.7 per cent, for work of ascent. 

Experiments on man, not cited in the above pages, in which 
the work was performed by turning a crank, have shown decidedly 
lower figures for the percentage utilization. 

Speed and Gait. — The energy expended by the horse in loco- 
motion at a walk was found to increase with the speed at the 
rate of 0.00334 cal. per meter and kilogram mass for each in- 
crease of 1 meter in the speed per minute. Kellner's mechanical 
analysis of the work of locomotion mentioned above divides it 
into two parts, viz., that expended in lifting the body of the 



514 PRINCIPLES OF ANIMAL NUTRITION. 

animal and that expended in imparting motion to the legs. The 
former portion is regarded as constant, while the latter portion 
would increase with the speed. The very close proportionality 
between the work thus computed and the total metabolism, as 
shown by the table on the preceding page, is a strong confirma- 
tion of the correctness of both methods and places the conclusion 
as to the influence of speed upon metabolism beyond reasonable 
doubt. It is to be remembered, however, that it is the total 
metabolism per kilogram and meter which increases with the speed. 
The percentage utilization of the energy, so far as the data at our 
command enable us to determine, apparently remains constant. 
Practically, however, it is the former fact which interests us, since 
the expenditure of energy in locomotion is comparable to that in 
internal work and has only an indirect economic value. A similar 
effect of speed on the metabolism in horizontal locomotion was 
observed by Zuntz * in experiments on man. In those with the dog, 
on the other hand, the variations in speed were between 64.2 and 
85.9 meters per minute, but no material difference in the metabo- 
lism due to locomotion was observed. 

In trotting, a horse expends much more energy per unit of hori- 
zontal distance than in walking. Thus, trotting at an average 
speed of 195 meters per minute (a little over 7 miles per hour), as 
compared with walking at an average speed of 90.16 meters per 
minute, gave the following results for the metabolism per kilo- 
gram mass and meter distance. 

Trotting 0.5478 cal. 

Walking 0.3666 " 

On the other hand, speed is, so to speak, obtained more econom- 
ically at the trot than at the walk. In the averages just given the 
speed was increased by 116 per cent., while the metabolism was in- 
creased by only 49 per cent. The same result is reached in another 
way by computing, by means of the factor given at the beginning of 
this paragraph (0.00334 cal.), the theoretical walking speed which 
would give a metabolism equal to the average metabolism in trot- 
ting. We find this to be 147 meters per second, as compared with 195 
meters at a trot. Moreover, it was found that at the trot the metab- 
olism did not increase with the speed, within the limits of the ex- 
* Arch. ges. Physiol., 68, 198. 



THE UTILIZATION OF ENERGY. 515 

periments. These, however, did not include speeds above 206 
meters per minute (about 1\ miles per hour), and the work was done 
on a tread-power, so that there was no air resistance. At this 
moderate speed it is not probable that the latter factor would be a 
large one, but it . is one which increases as the square of the 
velocity, so that at high speeds it constitutes the larger portion of 
the resistance. At high speeds, too, the muscles contract to a 
greater degree, thus decreasing their efficiency, and additional auxil- 
iary muscles are called into play, both directly and to aid the in- 
creased respiration. It is a matter of common experience that while 
a horse is able to travel for a number of miles consecutively at 6 to 
7 miles per hour, drawing a considerable load, he can maintain his 
highest speed for only a short time even without load, and does this 
only at the cost of largely increased metabolism. It is evident then 
that there is a limit beyond which an increase of trotting speed 
must increase the metabolism with comparative rapidity. 

Load.— Supporting a load on the back while standing was found 
to increase the metabolism of the horse No. Ill approximately in 
proportion to the load — that is, the metabolism computed per unit 
of mass (horse + load) increased but very slightly. In locomotion 
with a load the metabolism is, of course, increased, since the load 
as well as the body of the animal must be lifted at each step. The 
increase over the metabolism at rest and without load, both walking 
and trotting, was found in the case of Horse III to be somewhat 
greater (8-10 per cent.) than the increase in the mass moved 
(horse + load) . 

After making allowance for this increase in the work of locomo- 
tion, the efficiency in ascent with a load was found to be unaffected 
by the latter; that is, the energy expended in lifting a unit of mass 
(horse + load) through a unit of distance remained substantially 
the same. Indeed the figure obtained (36.2 per cent.) is slightly 
higher than that without load (34.3 per cent). Interesting indi- 
vidual differences in the above particulars were, however, observed 
between Horse No. Ill and some of the other animals experimented 
upon, particularly Nos. II and XIII, which form the subject of a 
succeeding paragraph. 

Species and Size of Animal. — In ascending a moderate grade, 
the efficiency seems to be about the same in the horse and in 



5 i6 



PRINCIPLES OF ANIMAL NUTRITION. 



man, while in the dog it is apparently somewhat less, as is seen 
from the following comparison: 





Grade, 
Per Cent. 


Efficiency, 
Per Cent. 


Man 


23 

10.7 
18.1 
17.2 


35.7 
34.3 
33.7 
30.7 


Horse 


a 


Dog 





The energy expended in horizontal locomotion, on the other 
hand, showed more marked differences, viz.: 





Speed, Meters 
per Minute. 


Energy Expended 

per Kg. Mass 
per Meter, Kgm. 


Dog 


78.57 

42.32-74.48 

78.00 


0.501 

0.211-0.334 

0.138 


Man 


Horse 





The relatively high figure for the dog is perhaps due in part to the 
considerable muscular effort apparently required (p. 499) to main- 
tain the erect posture. It has been shown by v. Hosslin,* however, 
by a mechanical analysis of the work of locomotion, that the latter 
does not increase as rapidly as the weight of the animal, but in 
proportion to its two-thirds power, or, in other words, approximately 
in proportion to the surface. If we compare the experiments upon 
different species of animals on this basis — that is, if we divide the 
total energy expended by the animal for locomotion by the product 
of the distance traversed into the two-thirds power of the weight 
— we obtain the following figures: 

Dog 1 . 501 kgm. 

Man 0.861-1.274 kgm. 

Horse 1 . 058 kgm. 

Computed in this way, the figures for the horse and those for man at 
a comparable speed (74.48 M. per min.) do not differ greatly, and 
v. Hosslin's conclusions are to this extent confirmed. The figures 
for the dog still remain higher than the others. If, in the case of 
* Archiv f. (Anatomie u.) Physiol., 1888, p. 340. 



THE UTILIZATION OF ENERGY. 517 

this animal, we compare the total metabolism in locomotion with 
that during standing instead of lying, as was done in the case of 
the horse, the figure is reduced to 1.303 kgm., or not much higher 
than in the case of man. It must be remembered, however, that 
the figures above given for man include the metabolism due to 
standing. 

Individuality. — Zuntz & Hagemann's investigations show that 
the efficiency of the horse is affected to a considerable degree by 
the individual differences in animals. The experiments whose 
results are summarized on p. 510 were upon a single animal 
(No. III). In addition to these a small number of experiments 
were made with several other animals, mostly old and more or less 
worthless ones, besides the considerable number upon Horse No. II 
previously reported by Lehmann & Zuntz.* The results are com- 
puted by the authors in terms of energy and corrected for speed 
upon the basis of the results obtained with Horse No. III. 

In a single case the work of ascent required slightly less expen- 
diture of energy than with Horse No. Ill, and in another case the 
work of horizontal locomotion, computed to the same five weight 
in proportion to the two-thirds power of the latter (see the oppo- 
site page) was also less than for Horse No. Ill, but as a rule these 
old, defective horses gave higher results. For ascent, omitting 
one exceptional case, the range was as follows : 

Per Kgm. of Work. 

Minimum 5 . 906 cals. = 39 . 84 per cent, efficiency 

Maximum 9.027 " =26.07 " " 

Horse No. Ill .. . 6.851 " =34.30 " " 
With one very lame horse (string-halt) the figures reached the 
maximum of 12.343 cals., or an efficiency of only 16.6 per cent. 

A similar range was observed in the results on horizontal loco- 
motion. Reduced to a speed of 78 M. per minute and to the live 
weight of No. Ill, the range was as follows: 

Per Meter and Kilogram Live Weight. 

Minimum 0. 284 cal. 

Maximum . 441 " 

Horse No. Ill 0.336 " 

* Landw. Jahrb., 18, 1. 



5*8 



PRINCIPLES OF ANIMAL NUTRITION. 



The very lame horse mentioned above gave a still higher figure, 
viz., 0.566 cal. 

A somewhat larger number of experiments with Horse No. XIII 
brought out the interesting fact that the increase in the metabo- 
lism caused by carrying a load on the back was markedly less than 
in the case of No. Ill, both at rest and in motion. 

PER KILOGRAM MASS (HORSE 4- LOAD). 





Without Load, 
cals. per Minute. 


With Load, 
cals. per Minute. 


Standing : 

Horse XIII 


15.990 
18.311 

cals. per Meter. 
0.389 
0.367 

0.553 
0.548 


14.670 
18.389 

cals. per Meter. 
0.388 
0.391 

0.488 
0.601 


" III 


Walking horizontally : 
Horse XIII 


" III 


Trotting Horizontally : 
Horse XIII 


" III 





While, without load, Horse No. XIII showed a greater metabo- 
lism, both while walking and trotting than did Horse No. Ill, the 
additional effort required for carrying a load was relatively less, 
so that in every case the metabolism per unit of mass, instead of 
increasing, remained unchanged or even diminished. The percent- 
age efficiency of the animal in ascending a grade was also not 
materially affected by the load, while with Horse No. Ill it ap- 
peared to increase slightly. 

The experiments with Horse No. II previously reported,* when 
recalculated f in the same manner as the later ones, likewise show 
interesting individual differences. For horizontal locomotion, 
after correcting for varying speeds, we have per kilogram mass 
(horse + load) the following: 





Horse No. II, 
cals. per Meter. 


Horse No. Ill, 
cals. per Meter. 


Walking without load 

" with load 


0.415 
0.385 
0.499 
0.415 


0.367 
0.391 
0.548 
0.601 


Trotting without load 

" with load 





* Landw. Jahrb., 18, 1. 



t Ibid., 27, Supp. Ill, 355 



THE UTILIZATION OF ENERGY. 



519 



As these figures show, No. II was decidedly inferior to No. Ill 
in walking without load. In trotting, on the other hand, he was 
somewhat the superior of No. Ill, or in other words the change 
from walking to trotting caused much less increase in his metabo- 
lism. Like No. XIII, he carried a load with decidedly less expendi- 
ture of energy than did No. III. For the forms of work in which 
the percentage efficiency could be measured the results were as 
follows, the grades, however being not exactly the same for No. II 
as for No. Ill: 





Horse No. II, 
Per Cent. 


Horse No. Ill, 
Per Cent. 


Ascending, moderate grade . . . 

heavier grade 

Draft, nearly horizontal 


33.2 
31.7 
29.0 
22.4 


34.3 
33.7 
31.3 
22.7 



It seems a fair presumption that such individual differences 
as those above instanced are caused, in large part at least, 
by differences in the conformation of the animals resulting from 
heredity or "spontaneous" variation. A strain of horses which 
has been bred and trained especially for the saddle through a 
number of generations might very naturally be expected to be 
more efficient in carrying a load than a strain which has been bred 
for speed in harness or strength in draft, while the latter might as 
naturally excel the former in efficiency at the trot or in draft. 
Similarly, a race of horses developed in a hilly country might be 
expected to be more efficient in ascending a grade than one in- 
habiting a flat region. It would seem, too, that these differences 
may be not inconsiderable. The results cited suggest an interest- 
ing line of thought and investigation for the student of breeding. 

Training and Fatigue. — It is a familiar experience that any 
unaccustomed form of work is much more fatiguing at first than it 
is later. This is due in part to the fact that in making unfamiliar 
motions more accessory groups of muscles are called into activity 
than are necessary later when more skill has been acquired. The 
experience of a learner on the bicycle is an excellent example of 
this. In the second place, however, simple exercise of a group of 



5 2 ° 



PRINCIPLES OF ANIMAL NUTRITION. 



muscles in a particular way seems to increase their average mechan- 
ical efficiency. 

Gruber,* in two series of experiments upon himself, obtained 
the following figures for the excretion of carbon dioxide during 
rest, horizontal locomotion, and hill climbing, all the trials being 
made .about the same length of time (four to five hours) after the 
last meal: 





Work of 
Ascent, 
Kgm. 


Carbon Dioxide 
Excreted in 20 
Minutes, Grms. 


Series I: 




9 . 706* 






19.390* 


Hill climbing without practice 


5892 
6076 


40.982 


Serws II (2 months later) : 


32.217 
12.833 






22.418 


" " after 14 days' practice 


7376 
7539 


38.832f 
31.001 



* Some carbon dioxide may have escaped absorption, 
t Some carbon dioxide lost. 

Schnyder f has confirmed and extended Gruber's results. In 
experiments in a treadmill upon two different subjects he ob- 
tained the following figures for the work performed per gram of 
carbon dioxide excreted in excess of that given off during rest : 

Kgm. 

( Without training 218. 13 

No ' \ After 2 months' training 253.18 

I Without training .• 243.93 

No. 2 < After 6 days' training 285.52 

| " 55 " " 349.40 

>T „ , . . . I Without training 302 . 76 

No.2 (second senes) j ^^ 4? dayg , training 404 39 

That the greater efficiency after training is not due solely to a 
diminished use of accessory muscles is shown by Schnyder's experi- 
ments on convalescents. His results were as follows: 

*Zeit. f. Biol., 28,466 
t Ibid., S3, 289. 



THE UTILIZATION OF ENERGY. 



5 21 



No. 1 — Climbing a hill 



No. 2— Treadmill 



No. 3— Treadmill 



Work per 
Gram, Car- 
bon Dioxide 
Kgm. 

j First trial 215 . 18 

\ 18 days later 306 . 18 

First trial 182 . 70 

2 days after first trial 248.34 



10 
12 
14 
15 
21 



253.74 

238.85 
210.87 
227.04 
227.50 



2\ months after first trial 441 . 17 

First trial 231 .24 

2 days after first trial 231 .24 

4 " " " " 286.25 



In walking the same distance (468 M.) No. 1 excreted the following 
excess of carbon dioxide over the rest value: 

First trial 4 . 505 grams 

A week later 3.690 " 

A month later 2. 780 " 

It appears from these results that the gradual strengthening of the 
muscles during convalescence results in a more economical per- 
formance of their work, largely independent of any special training 
for a particular kind of work. It seems a justifiable conclusion, 
therefore, that a part of the gain due to training arises from its 
direct effect in strengthening the muscles, as well as from the in- 
creased skill acquired in their use. Conversely, the effect of fatigue 
in increasing the relative metabolism, as shown by Loewy,* would 
seem to be in part a direct effect. Schnyder summarizes the matter 
in the statement that it is not the work itself, but the muscular 
effort required, which determines the amount of metabolism. 

In the case of domestic animals kept chiefly for work, however, 
we may safely assume that they are constantly in a state of training, 
and that the results obtained by Zuntz and his associates on the 
horse are applicable to work done by normal animals within the 
limits of the experimental conditions. 



* Arch. ges. Physiol., 49, 405. 



522 PRINCIPLES OF ANIMAL NUTRITION. 

Relative Values of Nutrients. — In the foregoing discussion 
it has been tacitly assumed that the stored-up energy of the pro- 
teids, fats, and carbohydrates of the body is all net available energy, 
ready to be utilized directly for the production of mechanical work. 
As we have seen, however, on previous pages, a school of physiolo- 
gists, of which Chauveau may stand as the representative, denies 
this, and holds that the fat in particular must be converted into 
a carbohydrate before it can become directly available. 

In discussing the source of muscular energy in Chapter VI it 
was shown that the recorded results as regards the nature of the 
material metabolized were insufficient to decide the question, since 
the final excretory products are qualitatively and quantitatively 
the same whether the fat is directly metabolized in the muscle or 
undergoes a preliminary cleavage in the liver or elsewhere in the 
body. The results as to energy, however, would be materially 
different in the two cases. The dextrose resulting from the cleavage 
of fat, according to Chauveau's schematic equation (p. 38), would 
contain but about 64 per cent, of the potential energy of the fat, the 
remainder being liberated as heat. We cannot, however, suppose 
that the energy of this dextrose can be utilized by the muscle any 
more completely than that of dextrose derived directly from the 
food. It follows, then, that the percentage utilization of the total 
energy metabolized during muscular work should be materially 
greater when the metabolized material consists largely or wholly of 
carbohydrates than when it consists chiefly of fat. By supplying 
food consisting largely of one or the other of these materials, it is 
possible to bring about these conditions, and a determination of 
the respiratory exchange and the nitrogen excretion will then 
afford a check upon the nature of the material metabolized and the 
means of computing the utilization of its potential energy. 

Investigations of this sort have been reported from Zuntz's 
laboratory. The earliest of these were by Zuntz & Loeb * upon a 
dog, the method being substantially the same as that with which 
the preceding pages have made us familiar. Their final results for 
the energy metabolized per kilogram and meter traveled (including 
the work of ascent) were: 

* Arch. f. (Anat. u.) Physiol., 1894, p. 541. 



THE UTILIZATION OF ENERGY. 523 



Diet. 



Respiratory 
Quotient. 



Energy, cals. 



Proteids only 

Chiefly fat 

" (body freed from carbohydrates by 

phloridzin) 

Much sugar with proteids 

" " and little proteids 



0.78 
0.74 

0.71 
0.83 
0.88 



2.58 
2.43 

2.71 
2.58 
2.63 



The differences are quite small, while, as Zuntz points out, if 
2.6 cals. represent the demand for energy per unit of work when 
carbohydrates are the source it should, according to Chauveau's 
theory, rise to about 3.68 cals. when the energy is derived exclu- 
sively from fat. 

Altogether similar results have been recently reported from 
Zuntz's laboratory by Heineman,* and by Frentzel & Reach, f in 
experiments on man. 

In Heineman's experiments the work, which was never exces- 
sive, consisted in turning an ergostat, the respiratory exchange 
being determined by means of the Zuntz apparatus and the total 
urinary nitrogen being also determined. From these data, reckon- 
ing 1 gram of urinary nitrogen equivalent to 6.064 liters of 
oxygen,J the average amount of energy metabolized on the vari- 
ous diets, and the proportion derived respectively from proteids, 
fats, and carbohydrates, is computed. By comparison with rest 
experiments the increments of oxygen and carbon dioxide due to 
the work were determined, and from these the energy consumed 
per kilogram-meter of work was calculated upon three different 
assumptions : first, that the proteid metabolism was not increased 
by the work; second, that it increased proportionally to the oxy- 
gen consumption; third, that as large a proportion of the energy 
for the work was furnished by the proteids as is consistent with 
the observed respiratory exchange. The results are summarized 
in the following table : 

* Arch. ges. Physiol., 83, 441. 

t Ibid., 83, 477. 

X Zuntz, Arch. ges. Physiol., 68, 204. 



5 2 4 



PRINCIPLES OF ANIMAL NUTRITION. 





Respira- 
tory 
Quo- 
tient. 


Total Energy 
Supplied by 


Energy per Kgm. 
of Work. 


Predominant Nutrient. 


Fat, 
Cals. 


Car- 
bohy- 
drates, 
Cals. 


Pro- 
teids, 
Cals. 


First 
As- 
sump- 
tion, 
cals. 


Second 

As- 
sump- 
tion, 
cals. 


Third 

As- 
sump- 
tion, 
cals. 


** It:: 

Carbohydrates. \ . ' ' 

As much proteids as 
possible 


0.783 
0.724 
0.805 
0.901 

0.796 


3829 
4422 
3414 
1543 

3381 


1379 

246 

1823 

3374 

1620 


163 
163 
139 
139 

377 


10.98 

9.39 

11.15 

10.67 

11.40 


9.35 
i6!63' 

11.27 


10.35 

9.27 

10.46 

10.37 

10.64 







The subject was not able to consume even approximately 
enough proteids to supply the demands for energy, so that the 
experiments are virtually a comparison of the utilization of fat and 
carbohydrates in different proportions. With the exception of the 
third group, the results seem to show that the energy of the fat 
metabolized was utilized, if anything, rather more fully than that 
of the carbohydrates. 

Frentzel & Reach experimented upon themselves, the work 
being done by walking in a tread-power; otherwise the methods 
were similar to those of Heineman. In computing the results of 
the experiments on a carbohydrate and a fat diet they assume that 
there was no increase in the proteid metabolism as a consequence 
of the work. For the experiments on a proteid diet they com- 
pute the results both on this assumption and also on the assump- 
tion of a maximum participation of the proteids in work produc- 
tion. Calculated in this way the total evolution of energy per kilo- 
gram weight and meter traveled was as given in the table on p. 525. 
The results show a slight advantage on the side of the carbo- 
hydrates, which in the case of Frentzel is regarded by the authors 
as exceeding the errors of experiment. They compute, however, 
that it is far too small to afford any support to Chauveau's theory. 

Zuntz * has recalculated Heineman' s results, using slightly 
different data but reaching substantially the same result. He 
shows, however, that they are affected by the influence of train- 
ing already discussed on p. 519. Arranging the experiments in 
chronological order, it becomes evident that the work was done 
* Arch. ges. Physiol., 83, 557. 



THE UTILIZATION OF ENERGY. 



525 



Respiratory 
Quotient. 



Energy per Kg. 
and Meter, cals. 



Frentzel — fat diet: 

First week 

Second week. . . . 



Average. 



Frentzel — carbohydrate diet : 

First week 

Second week 



Average. 



Frentzel — proteid diet: 
First assumption . . , 
Second assumption. , 

Reach — fat diet: 

First week , 

Second week 



Average. 



Reach — carbohydrate diet : 

First week 

Second week 



Average. 



0.766 

0.778 

0.773 



0.896 
0.880 

0.889 



0.799 

0.805 
0.766 

0.781 



0.899 
0.901 

0.900 



2.088 
2.049 

2.066 



1.932 
2.031 

1.980 



1.933 
1.824 

2.259 
2.034 

2.119 



2.202 
2.005 

2.086 



with increasing efficiency, largely independent of the food, and the 
fact that most of the experiments with fat came later in the series 
than those with carbohydrates largely, although perhaps not en- 
tirely, accounts for the observed difference in efficiency, while the 
low figure for proteids is accounted for by the fact that these were 
among the earliest experiments. A similar effect appears in the 
experiments of Frentzel & Reach, although it is less marked, since 
walking is a more accustomed form of work than turning a crank. 
On the whole, Zuntz concludes that these experiments warrant the 
conclusion that in work production the materials metabolized in 
the body replace each other in proportion to their heats of combus- 
tion — that is, in isodynamic and not isoglycosic proportions. 



THE UTILIZATION OF METABOLIZABLE ENERGY. 

ihe investigations just discussed give us fairly full data as to 
the utilization of the stored-up energy of the body in the produc- 
tion of external work, and this, as we have seen (p. 497), is sub- 
stantially equivalent to a knowledge of the utilization of the net 



526 PRINCIPLES OF ANIMAL NUTRITION. 

available energy of the food. These determinations by Zuntz and 
his co-workers, however, do not bring the energy recovered as 
mechanical work into direct relation with the energy of the food; 
that is to say (aside from such computations of available energy as 
those made by Zuntz & Hagemann* for the food of the horse), 
they do not tell us how much of the energy contained in a given 
feeding-stuff we may expect to recover in the form of mechanical 
work, but only what proportion of the stored-up energy resulting 
from the use of this feeding-stuff is so recoverable. 

It is the former question rather than the latter, however, which 
is of direct and immediate interest to the feeder of working animals. 
The feeding-stuffs which he employs are comparable to the fuel of 
an engine, and the practical question is how much of the energy 
which he pays for in this form he can get back as useful work. 

Methods of Determination. — Two general methods are open 
for the determination of the percentage utilization of the energy 
of the food. 

It is obvious that if we know the net availability of the energy 
(gross or metabolizable) of a given food material we can compute 
its percentage utilization in work production from the data of the 
foregoing paragraphs with a degree of accuracy depending upon 
that of the factors used. For example, if we know that the net 
available energy of a sample of oats is 60 per cent, of its gross energy, 
then if the oats are fed to a draft horse utilizing, according to Zuntz 
& Hagemann, 31.3 per cent, of the net available energy, it is obvious 
that the utilization of the gross energy of the oats is 60X0.313 = 
18.78 per cent. An entirely similar computation could of course be 
made of the percentage utilization of the metabolizable energy of 
the oats. 

Unfortunately, however, as we have already seen, our present 
knowledge of the net availability of the energy of feeding-stuffs and 
nutrients for different classes of animals is extremely defective, and 
extensive investigations in this direction are an essential first step 
in the determination of the percentage utilization of the energy 
of feeding-stuffs in work production by this method. Until trust- 
worthy data of this sort are supplied, results like those of Zuntz & 
Hagemann can be applied to practical conditions only on the basis 
* Landw. Jahrb., 27, Supp. Ill, 279 and 429. 



THE UTILIZATION OF ENERGY. 5 2 7 

of more or less uncertain estimates and assumptions regarding the 
expenditure of energy in digestion and assimilation such as those 
discussed in Chapter XI, § 3. 

The second possible general method for the determination of 
the percentage utilization of the energy of the food in work pro- 
duction is that employed in the determination of the utilization in 
tissue production. Having brought the animal into equilibrium as 
regards gain or loss of tissue and amount of work done with a suit- 
able basal ration, the material to be tested is added and the work 
increased until equilibrium is again reached. The increase in the 
work performed compared with the energy of the material added 
would then give the percentage utilization of the latter. 

The accurate execution of this method would require the em- 
ployment of a respiration apparatus or a respiration-calorimeter 
for the exact determination of the equilibrium between food and 
work, while the skill of the experimenter would doubtless be taxed 
in the endeavor to so adjust food and work as to secure either no 
gain or loss of tissue or equals of gain or loss in the two periods 
to be compared. Indeed, it may safely be said that exact equality 
would, as a matter of fact, be reached rarely and by accident, and 
that as a rule it would be necessary to correct the observed results 
for small differences in this respect. To make such corrections 
accurately, however, requires, as we have seen in § 1 of this 
chapter, a knowledge of the net availability and percentage utili- 
zation of the food, and we are thus brought back to the necessity 
for more accurate knowledge upon fundamental points. 

The extensive investigations of Atwater & Benedict * upon man 
appear to be the only ones yet upon record in which the actual 
balance of matter and energy during rest has been quantitatively 
compared with that during the performance of a measured amount of 
work. Unfortunately, however, the gains and losses of energy by 
the bodies of the subjects in these experiments were relatively 
considerable, while the experiments thus far reported seem to 
afford no sufficient data for computing the net availability of the 
food for maintenance or its percentage utilization for the production 
of gain. Moreover, the authors appear to regard the measurements 

* U. S. Department Agr., Office of Experiment Stations, Bull. 109 ; Mem- 
oirs Nat. Acad. Sci., 8, 231. 



528 PRINCIPLES OF ANIMAL NUTRITION. 

of the work done as not altogether satisfactory. In a preliminary- 
paper * Atwater & Rosa compute a utilization of 21 per cent. 
Inasmuch as they have not further discussed the question of the 
utilization of the food energy for work production it would seem 
premature to attempt to do so here. It may be remarked, however, 
that the figures given seem to indicate a rather low degree of effi- 
ciency for the particular form of work investigated (riding a station- 
ary bicycle). 

Wolffs Investigations. 

The horse, being par excellence the working animal, has natu- 
rally been the subject of experiments upon the relation of food to 
work. While as yet the respiration apparatus or calorimeter has 
not been applied to the study of this phase of the subject, two ex- 
tensive and important series of investigations have been made 
upon the work horse, viz., by Wolff and his associates in Hohen- 
heim and by Grandeau, LeClerc, and others f in Paris, in which the 
attempt has been made to judge approximately of the equilibrium 
between food and work from the live weight and the urinary nitro- 
gen. 

Grandeau's experiments were made for the Compagnie generate 
des Voitures in Paris, and were directed specifically toward a scientific 
investigation of the rations already in use by the company and to 
a study of the most suitable rations for the different kinds of ser- 
vice required of the horses. They were, therefore, while executed 
with the greatest care and exactness, largely "practical" in their 
aim. 

Wolff's experiments were made at the Experiment Station at 
Hohenheim and were broader in their scope, being directed largely 
to a determination of the ratio of (digested) food to work. The 
following paragraphs are devoted chiefly to an outline of Wolff's 
experiments, but with more or less reference also to Grandeau's 
results. 

Methods. — In discussing the effects of muscular exertion on 
metabolism in Chapter VI, mention was made of the interesting 

* Phys. Rev., 9, 248; U. S. Dept. Agr., Office of Experiment Station, Bull. 
98, p. 17. 

t L' alimentation du Cheval de Trait, Vols. I, II, III, and IV, and Annales 
de la Science Agronomique, 1892, I, p. 1; 1893, I, p. 1; and 1896, II, p. 113 



THE UTILIZATION OF ENERGY. 



529 



results obtained by Kellner regarding the influence of excessive 
work upon the proteid metabolism of the horse. It was there shown 
that when the work was increased beyond a certain amount there 
resulted a prompt increase of the urinary nitrogen and at the same 
time a steady falling off in the live weight. The method employed 
in Wolff's experiments, and which originated with Kellner, is based 
upon this fact. It may perhaps be best illustrated by one of 
Kellner' s earliest experiments,* in which starch was added to a 
basal ration, the results of which have already been referred to in 
Chapter VI (p. 199). 

In the first period the daily ration consisted of 6 kgs. of oats 
and 6 kgs. of hay, while in the second period 1 kg. of rice starch was 
added. Digestion trials showed that there was digested from these 
rations the following: 





Period I, 
Grms. 


Period II, 
Grms. 


Increase. 

Grms. 


Crude protein 


757.07 

636.10 

3874.36 

279.45 


750.53 

713.40 

4488.15 

275.43 


— 6 54 


" fiber 


+ 77 30 


Nitrogen-free extract 


+ 613 79 


Ether extract 


— 4 02 








5546.98 


6227.51 


+ 680.53 



The work was performed in a special sweep-power which was 
so constructed as to act as a dynamometer. With a uniform draft 
of 76 kgs., the daily work in the four subdivisions of the first 
period consisted of 300, 600, 500, and 400 revolutions respectively, 
while in the two subdivisions of the second period it was 800 and 
600 respectively. From the daily results for live weight and urinary 
nitrogen and from a comparison with another period in which 1.5 
kgs. of starch was fed, Kellner concludes that the maximum amounts 
of work which the animal could perform without causing an increase 
in its proteid metabolism and a decrease in its live weight were for 
the first period 500 revolutions and for the second period 700 revo- 
lutions. The difference of 200 revolutions, then, represents the 
additional work derived from the added starch. Two hundred 
revolutions with a draft of 76 kgs. equaled 438,712 kgm., to which 
is to be added the work of locomotion, estimated by Kellner (com- 
* Landw. Jahrb., 9, 670. 



53° PRINCIPLES OF ANIMAL NUTRITION. 

pare p. 539) at 100,000 kgm., making the total additional work 
538,712 kgm. Kellner compares this difference with the increased 
amount of nitrogen-free extract digested, 613.79 grams, neglecting 
the small differences in the other nutrients. As corrected in a later 
publication,* the results are as follows: 

613.79 grms. starch =2527. 601 Cals. = 1,071,698 kgm. 
538,712-1,071,698 = 50.27 per cent. 

If we base the calculation upon the difference in total organic 
matter digested, the percentage will of course be somewhat smaller. 

It was discovered later that the indications of the dynamometer 
used in these experiments and many subsequent ones were untrust- 
worthy, so that no value attaches to the percentage computed above, 
but it serves just as well to illustrate the method employed, and 
which was followed in the whole series of experiments. In brief, 
the attempt is to find in the indications of live weight and urinary 
nitrogen a partial substitute for the determination of the respira- 
tory products. As Kellner and Wolff do not fail to point out, the 
results are but approximations, and in any single experiment may 
vary considerably from the truth, but on the average of a large 
number of experiments it was hoped that satisfactory results might 
be reached. In later experiments rather more importance seems 
to be attached to the effects upon live weight than to those upon 
urinary nitrogen, but it should be noted that the live weight showed 
remarkably small variations from day to day, under the carefully 
regulated conditions of the experiments, and was quite sensitive 
to changes in the amount of work done. 

The experiments may be conveniently divided into three groups. 
The first of these f includes the years 1877 to 1886, inclusive, in which 
the work done was compared with the total digested food. The 
second J covers the experiments of 1886-1891, in which the digested 
crude fiber was omitted in computing the work-equivalent of the 
food, while the third group § includes the experiments of 1891-1894 
with a new and more accurate form of dynamometer. 

* Wolff, Grundlagen, etc., p. 89. 

t Grundlagen fiir die rationelle Fiitterung des Pferdes, 1886, 66-155; Neue 
Beitrage, Landw. Jahrb., 16, Supp. Ill, 1-48. 

% Landw. Jahrb., 16, Supp. Ill, 49-131, and 24, 125-192. 
§ Ibid., 24, 193-271. 



THE UTILIZATION OF ENERGY. 



531 



Experiments of 1877-1886.— During the years named, in addi- 
tion to the preliminary investigations necessary in working out the 
method, a large number of experiments were made on three different 
animals. The rations consisted largely of hay and oats in some- 
what varied proportions, together with smaller amounts of other 
feeding-stuffs. In three experiments on starch and four on oats a 
comparison of the increase in digested nutrients * with the in- 
creased work which could be done gave the following results : f 



Increase in Digested] 

Nutrients, 

Grms. 



Increase in Work Done 

at 76 Kg. Draft, 

Revolutions. 



Nutrients Equivalent 
to 100 Revolutions, 

Grms. 



Starch. 
Oats .. 



677.3 
577.0 



217 
175 



Average. 



312 
318 

315 



The Maintenance Requirement. — As already stated, it was 
discovered later that the dynamometer used was unreliable and 
gave too high readings, so that the above result cannot be em- 
ployed to compute the utilization of the energy of the added food. 
It does, however, in its present form, enable us to compute the 
maintenance requirements of the horse by subtracting from the 
total digested food the nutrients equivalent to the work performed 
(i.e., 3.15 gramsXthe number of revolutions). The results of such 
a computation made by Wolff J are given on p. 532. 

The actual live weights in these experiments were somewhat 
below the normal weights, which were regarded as being about 
533 kgs. for No. I, 500 kgs. for No. II, and 475 kgs. for No. III. 
Wolff considers the maintenance requirements to be independent 
of minor changes in weight, and on the basis of the above " normal " 
weights computes the maintenance requirements per 500 kgs. live 
weight as follows: 

Horse 1 4143 grams 

" II 4260 " 

" III 4167 " 

Average 4190 " 

* The algebraic sum of the differences in the single nutrients is used, and 
in this and the succeeding comparisons the digested fat is multiplied by 2.44. 
t hoc. dt., pp. 125-129. 
% hoc cit., pp. 99 and 132. 



53 2 



PRINCIPLES OF ANIMAL NUTRITION. 





No. of 
Experi- 
ments. 


Total 

Nutrients, 

Grms. 


Nutritive 
Ratio. 


Live 

Weight, 

Kgs. 


No. of 
Revolu- 
tions. 


Equiva- 
lent 
Nutrients, 
Grms. 


For 
Mainte- 
nance, 

Grms. 


Horse II: 

1881-82 

1882-83 

1883-84 


4 

7 
4 
6 


6305.6 

5831 . 1 

6748.3 
5920.2 


1:5.79 

1:6.64 
1:6.37 
1:7.26 


521 

477 
486 
457 


600 

546 

662 
567 


1890 

1720 
2085 
1786 


4416 

4111 
4663 
4134 


Average.. . 

Horse III: 

1881-82 

1882-83 

1883-84.... 
1S85 


17 

6 
6 
5 

4 


6078.4 

5313.8 
6061.3 
5734.8 
5761.2 


1:6.80 

1:7.16 
1:6.88 
1:7.55 
1:7.57 


473 

454 
469 
473 
473 


577 

404 
683 
580 
575 


1818 

1273 

2152 
1827 
1811 


4260 

4041 
3909 
3908 
3.50 


Average.. . 


21 


5717.8 


1:7.29 


467 


5a 


1766 


3952 



By means of a comparison of the results by groups * Wolff 
shows that the maintenance requirement as thus computed is appar- 
ently independent of the amount of work done and of the nutritive 
ratio, and from this uniformity concludes that the relative efficiency 
of the food for work production is unaffected by these factors, 
within the range of his experiments. 

A series of similar experiments on Horse No. Ill in 1 885-86, t 
computed in substantially the same way, gave results for the main- 
tenance ration agreeing well with those of earlier years, viz., 

Period 1 3934 grams total nutrients 

" II 3984 " 

" III and V.... , 4001 " 

" VII6 4094 " 

" VIII 4094 " 



Average 4021 " 

with an average live weight of 475 kgs., equivalent to 4230 grams 
per 500 kgs. In a succeeding period (IX), however, in which hay 
alone was fed, a decidedly higher result was obtained, viz., 4357 
grams per head, or 4586 grams per 500 kgs. 

* hoc. cit., pp. 135 and 137. 

f Landw. Jahrb., 16, Supp. Ill, 32. 



THE UTILIZATION OF ENERGY. 



533 



Experiments of 1886-91.— In the experiments thus far de- 
scribed, with the exception of the last, the proportions of grain and 
coarse fodder in the rations were not widely different, the latter 
furnishing on the average fully one half of the dry matter fed. 
Consequently the experiments were not calculated to bring out any 
difference in the nutritive value of the two such as is indicated by 
the results of the one trial with hay alone. 

Grain vs. Coarse Fodder for Maintenance. — The results 

obtained by Grandeau & LeClerc upon the maintenance ration of 

the horse when fed a mixture containing about 75 per cent, of 

grain fully confirm the indications of Wolff's trial with hay. 

Their experiments have been very fully discussed, and in part 

recalculated, by Wolff * in their bearing on this question. The 

three horses experimented on were fed two different amounts of 

the same mixture in several different thirty-day periods, eighteen 

such periods in all being available for comparison. In all of them 

the animals were led daily, at a walk, over a distance of about four 

kilometers. Wolff estimates the amount of work of locomotion by 

1 (W\ 
means of the formula ~-( — )v a and by subtracting the equivalent 

amount of nutrients from the total digested obtains the amount re- 
quired for maintenance. The results are as follows: 





No. of 
Experi- 
ments. 


Live 

Weight, 

Kgs. 


Digested 

Nutrients, 

Grms. 


Nutrients 
Equiva- 
lent to 
Work, 
Grms. 


For Maintenance. 




Per 
Head, 
Grms. 


Per 

500 Kgs., 
Grms. 


Heavier Ration : 

Horse I 

" II 

" III 


3 
5 
4 


416.6 
405.9 
439.0 


3553 
3432 
3625 


110 
108 
119 


3443 
3324 
3506 


4132 
4078 
3994 


Average 


420.5 

411.0 
441.2 


3537 

3060 
3310 


112 

108 
119 


3425 

2952 
3191 


4068 


Lighter Ration : 

Horse II 

" III 


2 

4 


3636 
3617 


Average 


426.1 


3185 


114 


3071 


3626 









The results, and particularly those on the lighter ration, which 
appeared ample for maintenance, are much lower than those com- 
* Landw. Jahrb., 16, Supp. HI, 73-81. 



534 



PRINCIPLES OF ANIMAL NUTRITION. 



puted in the previous paragraph. The difference is too great to be 
ascribed to experimental errors in estimating the small amount of 
work done, and can most reasonably be ascribed to the difference 
in the character of the ration. Apparently the horse, like cattle 
(p. 433), requires less digestible food for maintenance when the 
latter consists largely of grain than when it is chiefly or wholly coarse 
fodder. 

Direct experiments by Wolff * likewise show that the digestible 
nutrients of concentrated feed (oats) are more valuable for work 
production than those of coarse feed (hay). The experiments 
were made in the manner already described, the draft being uni- 
formly 60 kgs. Although the measurements of the work actually 
done are probably incorrect, it may be assumed to have been 
substantially proportional to the number of revolutions of the 
dynamometer. A ration of 3 kgs. of hay and 5.5 kgs. of oats served 
as the basal ration, to which was added in one case 4 kgs. of hay 
and in another 1£ kgs. of oats. The nutrients digested in each 
case and the equivalent amount of work secured were : 





Ration. 


Digested. 


53 a 


T3 

P4 


Protein, 
Grms. 


Crude 
Fiber, 
Grms. 


Nitrogen- 
free 
Extract, 
Grms. 


Ether 
Ex- 
tract, 
Grms. 


Total 

(Fat X 

2.4), 

Grms. 


5.0 


I-III 

v.... 


7 kgs. hay, 5.5 kgs. oats 
3 " " 5.5 " 


822 . 58 
626 . 46 


816.68 
422 . 74 


3889 . 64 
3068 . 46 


186.72 
184.78 


5973 . 62 
4561.13 


750 
350 




196.12 


393.94 


821.18 


1.94 


1412.49 
353.12 

5434.21 
4561.13 


400 








VI... 

v.... 


3 kgs. hay, 7 kgs. oats.. . 
3 " " 5.5 " " .. 

1 . 5 kgs. oats 


754.52 
626 . 46 


355 . 24 
393 . 94 


3719.24 
3068.46 


252.17 

184.78 


700 
350 




128.06 


- 67 . 50 


650.78 


67.39 


873 . 08 
249.45 


350 

















The relative value of the digested matter of hay and of oats for work 
production in these trials was thus approximately as 5 : 7. 

In the earlier experiments (p. 531) it was found that when oats 
or starch were added to a basal ration, approximately 315 grams 
of digested nutrients were required to produce the amount of 
work represented by 100 revolutions at 76 kgs. draft. Converting 
this result and the one just given for oats into kilogram-meters, 
Wolff computes that 100 grams of digested nutrients was equivalent, 
* Loc. cit., pp. 84-95. 



THE UTILIZATION OF ENERGY. 



535 



in round numbers, to 85,400 kilogram-meters in the earlier experi- 
ments and to 90,480 in the one just cited. While these figures are 
not correct absolutely, they are probably comparable, being ob- 
tained with the same apparatus. In the later experiment the 
work of locomotion is computed by Wolff's formula, which gives 
higher results than Kellner's. Taking this into account we may 
regard the agreement of the two equivalents as satisfactory. 

Value of Crude Fiber. — In all the experiments with con- 
centrated feeds the additional nutrients digested from the added 
food contained no crude fiber, the apparent difference, indeed, 
being in most cases, as in the above experiment, negative. When 
hay was added, on the other hand, over one fourth of the addi- 
tional nutrients digested consisted of crude fiber. If, now, we 
neglect this crude fiber and compare the work and the fiber-free 
nutrients we have 1018.55-^4.00 = 254.64 grams of fiber-free nutri- 
ents per 100 revolutions, or a figure corresponding almost exactly 
with that obtained for the fiber-free nutrients added in oats or 
starch. In other words, it would appear from this result that the 
digested crude fiber of hay is as valueless for work production as it 
appears to be for maintenance. 

If, however, the crude fiber is valueless both for maintenance 
and work, then by omitting it altogether from our computations we 
ought to get results for the maintenance ration and for the ratio of 
nutrients to work which are independent of the proportion of grain 
to coarse fodder in the ration. Confirmatory evidence of this sort 
is abundantly furnished by Wolff's experiments and likewise by 
the results of Grandeau on maintenance. Taking first the averages 
of the experiments of 1877-1886 (p. 532) we have — 





Nutrients Digested. 


No. of 
Revolu- 
tions at 
76 Kgs. 


Equiva- 
lent 
Nutrients, 
Grms. 


Fiber-free Nutrients 
for Maintenance. 






Without 
Crude 
Fiber, 

Grms. 






Total, 
Grms. 


Crude 
Fiber, 
Grms. 


Per Head, 
Grms. 


Per 500 
Kgs., 
Grms. 


Horse I 

" II ... . 
" III . . . 


6306 
6078 
5718 


815 
978 
809 


5491 
5100 
4909 


600 
577 
561 


1890 
1818 
1766 


3601 

3282 

143 


3378 
3282 
3306 
















3322 



















536 



PRINCIPLES OF ANIMAL NUTRITION. 



The results of the series made in 1885-86 on Horse No. Ill 
(p. 532), computed in the same way, give the following as the 
amounts of fiber-free nutrients required for maintenance : 





Per Head. 
Grms. 


Per 500 Kgs. 

Live Weight, 

Grms. 


Period I 


3270 
3186 
3242 
3342 
3316 
3170 


3442 
3353 
3413 
3549 
3490 
3335 


" II 


" III and V 

" VIL 

" VIII 


" IX 


Average 


3254 


3430 





From Grandeau's experiments (p. 533), by the same method, we 
have for the lighter ration the following: 





Per Head, 
Grms. 


Per 500 Kgs. 

Live Weight, 

Grms. 


Horse II 


2732 
2935 


3324 
3328 


" III 


Average 




3326 







Finally, for the series of experiments by Wolff, just discussed, 
upon the relative value of the digested matter of oats and of hay, 
and from which the conclusion as to the lack of value of the crude 
fiber was drawn, by computing backwards, we get figures for the 
fiber-free nutrients required for maintenance which not only agree 
with each other, as they necessarily must, but also with those of 
the earlier experiments. The results are: 





Per Head, Grms. 


Per 500 Kgs Live 
Weight. Grms. 


Period I-III 

" IV 


3175 
3275 
3180 
3196 


3342 
3429 
3329 
3364 


V 


" VI 


Average „ 




3366 







THE UTILIZATION OF ENERGY. 537 

Wolff's conclusions from these results * are — 

1. The digested crude fiber is apparently valueless, both for 
maintenance and for work production. 

2. The remaining nutrients may be regarded as of equal value 
whether derived from grain or coarse fodder. 

3. The maintenance of a 500-kg. horse requires approximately 
3350 grams per day of fiber-free nutrients. 

Wolff's subsequent experiments up to 1891 f gave results con- 
firmatory in general of the above conclusions. Particularly was 
this the case when the work of locomotion was computed by Kell- 

1 /W\ 
ner's formula and not by the formula -( — )v' i . The work done 

2\0/ 
(expressed in number of revolutions of the dynamometer) per 100 
grams of fiber-free nutrients was reasonably uniform and agreed 
well with the results previously obtained, while the fiber-free 
nutrients required for maintenance likewise agreed with the results 
given above. On the other hand, the inclusion of the digested 
crude fiber in the computations gave in many cases strikingly 
discordant results. In view of the unreliability of the measurement 
of the work no conclusions can be drawn as to the percentage 
utilization of the energy of the food, and it seems unnecessary to 
describe the individual experiments. 

A discussion by Wolff t of the results of some of the experi- 
ments by Grandeau in which work was done, although rendered 
uncertain by the difficulty in estimating the work of locomotion at 
varying velocities, and by the changes in live weight of the animals, 
seems to indicate that they also confirm Wolff's conclusions. 

Significance of the Results. — In drawing his conclusions 
Wolff is careful to say that the digested crude fiber is apparently 
valueless, and while calling attention to Tappeiner's then recent 
results on the fermentation of cellulose in the digestive tract as 
probably explaining its low nutritive value he points out that 
other ingredients of the food may also undergo fermentation. He 
therefore holds fast to the fact actually observed, viz., the lower 
nutritive value of the digested matter of coarse fodder compared 

* Loc. cit., p. 95. 

t Landw Jahrb., 24, 125-192. 

% Ibid., 16, Supp. Ill, 110-126. 



538 PRINCIPLES OF ANIMAL NUTRITION. 

with that of grain, and virtually regards the amount of crude 
fiber as furnishing a convenient empirical measure of the difference. 
In the light of our present knowledge this reserve seems amply 
justified. The difference in the value of coarse fodder and grain 
we should now regard as arising largely from the difference in the 
amounts of energy consumed in digestion and assimilation. Refi- 
ner's experiments on extracted straw discussed in the previous 
section have shown, however, that with cattle this difference 
is by no means determined by the simple presence of more or less 
crude fiber, but is related rather to the physical properties of the 
feeding-stuff, while Zuntz (see p. 392) has shown that the same 
factor largely affects the work of mastication in the horse. That 
the nutritive value of the rations in Wolff's experiments was pro- 
portional to the amount of fiber-free nutrients which they contained, 
or, in other words, that the energy expended in digestion, etc., was 
proportional to the digested crude fiber, is explained by the limited 
variety of feeding-stuffs employed. The coarse fodder was meadow 
hay with, in some cases, an addition (usually relatively small) of 
straw, while the grain was commonly oats, part of which was in some 
instances replaced by maize, beans, barley, flaxseed, or oil-meal, 
while starch was added to the ration in a number of trials. The 
larger part of the work of digestion, under these circumstances, was 
probably caused by the coarse fodders, viz., hay and straw, while the 
digested crude fiber was likewise derived chiefly or entirely from 
these substances. Such being the case, it follows that the loss 
of energy through digestive work would be in general proportional 
to the amount of crude fiber in the ration. The essential point in 
Wolff's experiments is that the omission of crude fiber renders the 
results concordant, and this is as well explained in the manner just 
indicated as by the estimate of Zuntz & Hagemann that the work 
of digesting and assimilating crude fiber consumes the equivalent 
of its metabolizable energy. 

Experiments of 1891-94. — In the dynamometer employed by 
Wolff the resistance was produced by the friction of metallic sur- 
faces. A copy of his dynamometer was employed by Grandeau & 
LeClerc in their investigations at Paris, and these experimenters 
found* that the measurement of the work was subject to large errors, 

* Fourth Memoir, p. 49. 



THE UTILIZATION OF ENERGY. 539 

particularly in experiments at a trot, owing to the continual changes 
in the friction. Wolff believes that in his experiments, all made 
at a rather slow walk, the errors are less, but admits that they are 
sufficient to deprive his computations of utilization of all val e. 

Grandeau & LeClerc, however, were successful in improving 
the dynamometer, by the addition of an integrating apparatus,* so 
that its measurements of the total work were satisfactory, and this 
.apparatus was added to Wolff's dynamometer in 1891. Before that 
•date, therefore, Wolff's experiments, while of great value in many 
other respects, afford no trustworthy direct data as to the utili- 
zation of the energy of the food for work production, although, as 
we have just seen, they afford some information on subsidiary 
points. From 1891, however, we may regard the measurements of 
the work done on the dynamometer as reasonably accurate. 

Corrections. — Unfortunately, in the light of subsequent 
investigation, the same is not true of some of the other factors 
entering into the comparison, particularly the work of locomotion 
and the metabolizable energy of the food. 

In all his later experiments Wolff computes the work of hori- 

1 fW\ 

zontal locomotion per second by means of the formula -= I — jv 2 , 

in which W equals the weight of the animal, g the force of gravity, 
and v the velocity per second. Zuntz's experiments, however, 
appear to show that this formula gives too high results, the error 
increasing with the velocity, and Wolff t himself recognizes the truth 
of this for higher speeds. According to Zuntz's determinations 
(p. 512), Ke'llner's method of computation gives results agree- 
ing quite closely with those computed from his respiration experi- 
ments. Under the conditions of Wolff's experiments this corre- 
sponds quite closely to 50,000 kgm. per 100 revolutions of the 
dynamometer, and in the comparisons which follow this amount 
has been substituted for that computed by Wolff, thus reducing 
materially the figures for the total work performed. 

Wolff estimates the metabolizable energy of the food, on the 
basis of Rubner's results, by multiplying the digested fat by 2.4, 
adding the remaining digested nutrients, and reckoning the total 

* Ann. Sci. Agron., 1881, I, 464. 

f Landw. Jahrb., 16, Supp. Ill, 119. 



54° PRINCIPLES OF ANIMAL NUTRITION. 

at 4.1 Cals. per gram. As we have seen, however (Chapter X),. 
this figure is probably too high for herbivora, although exact figures 
for the horse are not yet fully available. Approximately, however, 
we may estimate the metabolizable energy of the several digested 
nutrients as follows (p. 332): 

Protein 3 . 228 Cals per gram 

Crude fiber 3.523 " " " 

Nitrogen-free extract 4.185 " " " 

Ether extract 8.572 " " " 

Zuntz * estimates the metabolizable energy of the total nutri- 
ents (including fat X 2.4) at 3.96 Cals. per gram. This figure is 
probably somewhat high, especially for rations containing much 
crude fiber or ether extract, but may serve the purpose of approxi- 
mate calculations. 

Experiments on Single Feeding-stuffs. — Comparatively few 
of the experiments admit of a direct computation of the utiliza- 
tion for a single feeding-stuff, since in most cases the amounts of 
two or more feeding-stuffs were varied simultaneously. As an 
example of the former class we may take Periods I and II of the 
experiments of 1892-93. In Period I the ration consisted of 7.5 legs, 
of hay and 4 kgs. of oats per day, while in Period II the oats were 
increased to 5.5 kgs. The quantities of nutrients digested and the 
metabolizable energy of the difference between the two rations 
(computed by the use of the factors just given) were — 





Protein, 
Grms. 


Crude 
Fiber. 
Grms. 


Nitrogen- 
free 
Extract, 
Grms. 


Ether 

Extract, 

Grms. 


Total 

Nutrients, 
Grms. 


Period II 

" I 


1022.4 

847.8 


849.6 
819.9 


4152.8 
3598.4 


175.8 

137.1 


6446 . 6 
5595.3 


Difference .... 
Equiv. energy . . . 


174.6 

Cals. 
564 


29.7 

Cals. 

105 


554.4 

Cals. 

2320 


38.7 

Cals. 

332 


851.3 

Cals. 

3321 



In Period I (20 clays) the daily work consisted of 300 revolutions 
of the dynamometer. With this amount of work the live weight 
of the horse underwent very little change, but there was a material 

* Landw. Jahrb., 27, Supp. Ill, 418. 



THE UTILIZATION OF ENERGY. 



541 



gain of nitrogen, so that Wolff estimates that the work might have 
been increased to 350 revolutions. In Period II (23 days) the 
daily work was increased to 450 revolutions and the same behavior 
was observed, while a further increase to 500 revolutions during 
the last ten days checked the gain of nitrogen without causing a 
decrease in live weight. Taking 350 and 500 revolutions respec- 
tively as representing the maximum amount of work that could be 
done on the two rations, the equivalent of the oats added may be 
computed as follows: 



» 


Revolutions. 


Equivalent 
Work, 
Kgm. 


Period II 


500 
350 


1 030 687 


" I 


722,678 




Difference 


150 


308 009 


Work of locomotion for 150 revolutions 


75,000 








Total difference 


383,009 
903 Cals. 


Equal to 











The percentage utilization was therefore 903 -r- 3321 = 27.2 per cent. 

The above figures serve to exemplify the general method of 
computation and likewise to illustrate the weak points in Wolff's 
experiments, viz., the uncertainty in the determination of the work 
of locomotion and the impossibility of demonstrating the equilib- 
rium of food and work without the use of the respiration apparatus 
or calorimeter. 

Out of the whole number of experiments between 1891 and 1894, 
seven admit of a comparison of this sort, viz., four on oats, two on 
straw, and one on beans. Upon making the computations, how- 
ever, the results are found to be so exceedingly variable (the range 
for oats, e.g., being from 16.89 to 63.96 per cent.) as to demonstrate 
that the data of Wolff's experiments are not sufficiently exact to be 
used in this way, and that- the apparently reasonable result just 
computed is purely accidental. 

Utilization of Fiber-free Nutrients. — But although Wolff's 
results do not enable us to compute the percentage utilization of 
single feeding-stuffs, if we accept provisionally his conclusions re- 
garding the non-availability of the crude fiber they afford data for 
numerous computations of the utilization of the fiber-free nutrients, 



542 



PRINCIPLES OF ANIMAL NUTRITION. 



and these computations in turn supply a check upon the hypoth- 
esis of the non-availability of crude fiber. 

Wolff makes the comparison by deducting from the total fiber- 
free nutrients 3300 grams per 500 kgs. live weight for maintenance 
and comparing the energy of the remainder with the amount of 
work done. In the following tabulation of his results this method 
has been pursued. For the energy of the fiber-free nutrients, 
Zuntz's figure (3.96 Cals. per gram) has been used and the work of 
locomotion has been estimated at 50,000 kgm. per 100 revolutions 
of the dynamometer (compare p. 539). 



Period. 



He 
III 
IV. 



la-a 
lib. 
III. 
IV. 

V. . 



I... 
II.. 
Ill . 

IV6. 

V. . . 
Vic. 



I. . 
III. 

v.. 

VI. 



Ration. 



1891-92. 

Hay, 7.0 kgs.; oats. 4.5 kgs. 

" 7.0 " " 5.5 " . 

" 4.5 " " 7.0 " . 

Average 



1892. 
Hay, 7 . 5 kgs. ; oats, 4 . kgs. ; . 



4.5 
" 4.5 
" 4.5 
" 7.5 
Average 



5.5 " straw 
grain, 5.0 kgs. ; 

" 5.0 " 
oats, 4.5 " 



5 kgs 
5 " 



Hav 


7 


5 kgs. 


oats 




7 


5 ' 








6 


' 








6 


' 








4 


' 








4 


' 







1892-93. 
4.0 kgs. 
5.5 " . 
5.5 " 
5.5 " 
7.5 " 
7.5 " 



straw, 1 kg. 
1 " . 

" 2 kgs 



Average 



1893-94. 

Hay, 6.5 kgs.; oats. 4.0 kgs.; straw, 1.0 kg. 

" 3 0" " 7.0 " " 2.5kgs 

3.0 " grain, 7.0 " " 2.5 " . 

" 3.0 " " 6.5 " " 2.5 " . 

Average 



Fiber-free 

Nutrients 

Minus 3300 

Grms. 



Grms. Cals 



1 424 
1,990 
2,259 



1 ,775 
1.873 
1,521 
1,860 
1 903 



1,475 
2,297 
1,670 
2,036 
2,577 
2,692 



5,639 
7,881 
8,945 



7,026 
7.416 
6,023 
7,365 
7,537 



5.841 
9,095 
6.613 
8.063 
10,210 
10,660 



Work Done. 



Kgm. Cals. 



931,676 2,197 
1,129,568'2,663 
1,094,328 2,581 



1,074,802 2,535 

1,153,81312,720 

912,4542,152 



1,186,577 
1,188,388 



897,678 
1,280,687 

905,568 
1,167,127 
1,421,285 
1,549,620 



1,607 6,362 900,267 
2,580 10,220 1,549,262 
2,560 10. 140J 1,545 ,702 
2,880 11,420 1,673,786 



2,709 
2,803 



2 a 



38.95 
33.79 
28.86 
33.16 



36 . 07 
36.68 
35 . 73 
38.00 
37.18 
36:77 



2,116 36.24 
3 ,024! 33. 20 
2,135132.28 
2,752134.14 
3, 352 '32. 85 
3,655 34.28 
33 . 74 



2,122 33.36 
3,653 35.76 
3, 645 ! 35. 95 
3,94834.61 
,35.05 



In every instance but one the utilization as thus computed 
exceeds 31.3 per cent. In other words, the energy of the body 
material which, according to Zuntz & Hagemann's results, must 
have been metabolized to produce the amount of work done exceeds 
considerably the amount computed to be available from the food. 
There being no reason to question the substantial accuracy of Zuntz 
& Hagemann's factor, this means, of course, that if the food and 
work were in equilibrium our estimates of the energy available from 



THE UTILIZATION OF ENERGY. 



543 



the food are too low. Either 3300 grams of fiber-free nutrients 
(13,068 Cals.) is too large an allowance for maintenance, or the 
assumption that the energy of the digested crude fiber is substan- 
tially equivalent to the work of digestion and assimilation is erro- 
neous, or, finally, the figure of 3.96 Cals. per gram of digested nutri- 
ents is too small. As regards the latter possibility, while it may 
be conceded that the energy per gram of digested matter will vary 
somewhat in different experiments, the difference will be too small 
to materially affect the result. The uncertainty regarding the 
maintenance requirement may be readily eliminated by a computa- 
tion based on the differences between the several periods, thus afford- 
ing, to a degree at least, a test of the correctness of Wolff's hypothe- 
sis regarding the crude fiber. The following table contains the 
results of such comparisons. In each series the period with the 
least amount of digested food (fiber-free) has been compared with 
the other periods of the same series. 





Metabolizable 

Energy of 

Fiber-free 

Nutrients. 

Cals. 


Work, 
Cals. 


Utilization, 
Per Cent. 


1891-92. 
Period III 


20,949 
18,707 


2663 
2197 




" He 








Period IV 


2,242 

22,013 
18,707 


466 

2581 
2197 


20.79 


" He 








1892. 
Period la—d 


3,306 

20,094 
19,091 


384 

2535 

2152 


11.62 


" III 












1,003 

20,484 
19,091 


383 

2720 
2152 


38.19 


" III 








Period IV 


1,393 

20433 
19,091 


568 

2799 
2152 


40.77 


" III 










1,342 


647 


48.21 



544 



PRINCIPLES OF ANIMAL NUTRITION. 





Metabolizable 

Energy of 

Fiber-free 

Nutrients, 

Cals. 


Work, 
Cals. 


Utilization, 
Per Cent. 


1892. 
Period V 


20,605 
19,091 


2803 
2152 




" III 








1892-93. 
Period II 


1,514 

22,163 
19,295 


651 

3024 
2126 


43.00 


" I and III.... 








Period IV6 


2,868 

21,131 
19,295 


898 

2752 
2126 


31.31 


" I and III.... 








I and III 


1,836 

23,278 
19,295 


626 

3352 
2126 


34.10 






Period Vic 


3,983 

23,728 
19,295 


1226 

3655 
2126 


30.78 


" 1 and III 








1893-94. 
Period III 


4,433 

23,288 
19,430 


1529 

3653 
2122 


34.48 


" I 








Period V 


3,858 

23,208 
19,430 


1531 

3645 

2122 


39.68 


" I 








Period VI 


3,778 

24,488 
19,430 


1523 

3948 
2122 


40.31 


I 








Totals and averages, ex- 
cluding 1891-92 


5,058 
31,066 


1826 
11,408 


36.10 
36.73 



With the exception of the experiments of 1891-92, which were 
the first with the new form of dynamometer and which Wolff con- 
siders unsatisfactory, we have but two cases in which the apparent 
utilization does not exceed 31.3 per cent. Having eliminated the 
uncertainty as to the maintenance ration, and the figures for the 
energy of the food being regarded as substantially correct, this can 



THE UTILIZATION OF ENERGY. 545 

mean only one of two things, viz., that the figures for the work done 
are too high or that the deduction on account of the crude fiber is 
too great. 

That a determination of the equivalence of food and work by 
Wolff's method is subject to considerable uncertainty in an indi- 
vidual case is obvious, but there seems to be no apparent reason 
why it should be uniformly overestimated. The measurement of 
the work was made with great care, and while the work of locomo- 
tion is an estimate, its close agreement with the results of Zuntz & 
Hagemann (p. 539) renders it unlikely that it is seriously in error. 

It would appear, then, that with the rations used in these ex- 
periments the energy required for digestion and assimilation was 
less than the energy of the digested crude fiber. How much less it 
was, however, unfortunately does not appear, and we are obliged 
to content ourselves for the present with this negative conclusion. 

Zuntz & Hagemann's Computations. — These investigators * 
have recalculated Wolff's results in a still different manner. In- 
stead of taking for the amount of work equivalent to the ration the 
figures given by Wolff, which, as already explained, are to a certain 
extent estimates, they take the amount of work actually performed 
in each case and correct for the observed gain or loss of live weight. 
This method is in conception more scientific than Wolff's, pro- 
vided the requisite correction can be accurately estimated. As the 
basis for such an estimate, Zuntz & Hagemann take an early experi- 
ment by Wolff,f from which they compute that one gram loss of 
live weight is equivalent to one half revolution of the dynamometer 
(at 76 kgs. draft). From the same experiment they compute the 
mechanical equivalent of one revolution as 2694 kgm. This, how- 
ever, aside from the fact that it is the result of a single series of 
experiments, was obtained with the old form of dynamometer, 
whose indications, as we have seen, were too high, but the later 
experiments unfortunately are not reported in a way to permit of 
an estimate of the difference. 

Taking the correction, then, as estimated, Zuntz & Hagemann 
divide Wolff's experiments into two groups, viz., those in which the 
work was 400 or less revolutions and those in which it was more 

* Loc. cit., pp. 412-422. 
f Grundlagen, etc., p. 80. 



546 



PRINCIPLES OF ANIMAL NUTRITION. 



than 400 revolutions. Comparing the averages of these two groups, 
they obtain the following: 





Total 

Digested 

Nutrients, 

Grms. 


Work, Kgm. 


Loss of 

Live 

Weight, 

Grms. 


Heavier work (18 experiments) 


6236 
5851 


1,415,755 
995,225 


179.5 


Lighter " (13 " ) 


7.3 






Difference 

Correction for loss of weight 


385 


420,530 
231,922 


172.2 










188,608 





According to this computation, the 385 grams of added nutrients 
enabled 188,608 kgm. of work to be performed. At 3.96 Cals. per 
gram the metabolizable energy of the added nutrients equals 1524 
Cals. From this, according to Zuntz & Hagemann, is to be de- 
ducted 9 per cent, for the work of digestion and also 2.65 Cals. 
for each gram of total crude fiber in the added food. On this 
basis we have the following: 





Weight, 

Grms. 


Energy. 
Cals. 




385 

2338 
2356 

-18 


1524 


Average crude fiber fed : 

Heavier work 


Lighter work 


Difference 


Equivalent energy 




-48 


Work of digestion (1524 X 0.9). . 




137 


Deduction 




89 
1435 


Available energy 




Work done (188,608 -*- 424)... . 





445 









The work done is 31 per cent, of the computed available energy of 
the food, a figure corresponding very closely with the 31.3 per 
cent, found by Zuntz & Hagemann. 

The difference in the average amount of crude fiber fed in the 
two groups of experiments is so small that the estimate for the 



THE UTILIZATION OF ENERGY. 547 

energy required by its digestion hardly affects the computation. 
What the result appears to show is that the estimate of 9 per 
cent, for the digestion and assimilation of the fiber-free nutrients 
is approximately correct. 

The difference in the amount of digested crude fiber was some- 
what greater than that in the total amount. If we make the com- 
parison of the two averages on the basis of the fiber-free nutrients 
in the same manner as in previous cases we have — 

Fiber-free nutrients : 

Heavier work 5524 grams 

Lighter work 5086 " 

Difference 438 " 

Equivalent energy 1735 Cals. 

Energy of work 445 " 

Utilization 25 . 65 per cent. 

Apparently a considerable amount of energy was required for 
the work of digestion and assimilation in addition to that equiva- 
lent to the digested crude fiber, a result which seems to conflict 
with the conclusions drawn from a discussion of the same experi- 
ments in the preceding paragraph. The apparent discrepancy lies 
in the determination of the amount of external work equivalent 
to the added nutrients. Wolff, as we have seen, after securing 
an approximate constancy of live weight, corrects the measured 
amount of work in accordance with his judgment of the amount 
which would have been equivalent to the ration given and relies on 
the "might of averages" to overcome the inherent uncertainties of 
his method. Zuntz & Hagemann, on the other hand, reckon with 
the measured amount of work, but are then compelled to correct 
their final result for the loss of live weight, and unfortunately this 
correction is relatively a very large one (over 50 per cent.) and rests 
upon a rather uncertain basis. While it would perhaps be pre- 
sumptuous to attempt to decide the relative value of the two methods 
and the probability of the divergent conclusions based on them, one 
can hardly avoid feeling that the trained judgment of the actual 
experimenter is a safer reliance than such a relatively large cor- 
rection computed by a critic. 



548 PRINCIPLES OF ANIMAL NUTRITION. 

In any case it is obvious that while the extensive researches 
of Zuntz and his associates afford very reliable data as to the 
ratio between the energy liberated in muscular work and the 
amount of external work accomplished, or, in other words, as to 
the utilization of the net available energy of the food, we have as 
yet, notwithstanding the vast amount of work done by Wolff and 
his co-laborers and others, but very fragmentary and uncertain 
data as to the utilization of the metabolizable energy of the food for 
work production. 



APPEKDIX. 



TABLE I. METABOLIZABLE ENERGY OF COARSE FODDERS. 





*3 

1 

< 




Organic 
Matter 
Eaten. 


Energy of 


Metabolizable 
Energy. 


Feed Added. 


ED 

a 
o 

o 
Eh 


TS 

eu 

<u 
Ph 

IS 

d 


Food, 
Cals. 


Feces, 
Cals. 


Urine 
(Cor- 
rected), 
Cals. 


Methane, 
Cals. 


Total, 
Cals. 


Per 
Grm. 
Or- 
ganic 
Mat- 
ter, 
Cals. 


Meadow hay V ■! 


F 
F 

G 
G 

H 
H 

H 
H 


1 
3 

2 
3 

2 

4 

7 
4 


9475 
6630 


6024 
3175 


44821.2 
31327.8 


16323.7 
9599.2 


2113.3 
1530.0 


3250.6 
2560.7 


23133.6 
17637.9 




Difference .... 
Correction .... 


2845 

9405 
6651 


2849 

5950 
3206 


13493.4 
+ 19.0 


6724.5 
+5.9 


583.3 
+ 0.9 


689.9 

+ 1.5 


5495 . 7 
+ 10.7 




Percentage . . . 
Meadow hay V j 


13512.4 
100.00 

43811.3 
30750.7 


6730.4 
49.81 

15336.3 
9491.5 


584.2 
4.32 

1916.1 
1359.6 


691.4 
5.12 

3432.1 

2524.7 


5506.4 
40.75 

23126.8 
17374.9 


1.933 


Difference .... 
Correction. . : . 


2754 

9527 

6402 

3125 

9743 
6402 


2744 

6323 
3198 


13060.6 
-45.4 


5844.8 
-14.0 


556.5 
-2.0 


907.4 
-3.7 


5751.9 
-25.7 




Percentage . . . 
Meadow hay VI s 


13015.2 
100.00 

45255.8 
30338 . 1 


5830.8 
44.80 

14103.7 
8574.9 


554.5 
4.26 

2576.3 
1795.0 


903.7 
6.94 

3306.6 
2579.4 


5726.2 
44.00 

25269.2 
17388.8 


2.087 


Difference .... 
Correction .... 


3125 

6495 
3198 


14917.7 
-8.9 


5528.8 
-2.5 


781.3 
-0.5 


727.2 
-0.8 


7880.4 
-5.1 




Percentage . . . 
Meadow hayVI j 


14908.8 
100.00 

46275.0 
30338.1 


5526 . 3 
37.07 

14104.8 
8574.9 


780.8 
5.24 

2593.0 
1795.0 


726.4 

4.87 

3564.2 
2579.4 


7875.3 
52.82 

26013.0 

17388.8 


2.520 


Difference. . . . 
Correction.. . . 


3341 


3297 


15936.9 
-208.3 


5529 . 9 
-58.9 


798.0 
-12.3 


984.8 
-17.7 


8624.2 
119.4 




Percentage .. . 


15728.6 
100.00 


5471.0 
34.78 


785.7 1 967.1 
5.00 ! 6.15 


8504.8 
54.07 


2.580 



549 



55° 



APPENDIX. 



TABLE I (Continued). 



Feed Added. 



Meadow hay VI j 

Difference. . . . 
Correction. . . . 

Percentage . . . 

Oat straw II . . -j 

Difference . . . 
Correction. . . . 

Percentage . . . 

Oat straw II. . j 

Difference 
Correction. . . . 

Percentage. . . 

j 



Wheat straw I 



Difference 
Correction. . . . 



Percentage . . . 

Wheat straw I j 

Difference 
Correction 

Percentage . . . 

Extracted rye j 
straw I 

Difference . . . 
Correction . . . 

Percentage . . . 

Extracted rye j 
straw ( 

Difference. . . . 
Correction. . . . 

Percentage . . . 



Organic 
Matter 
Eaten. 



9539 

G458 



3081 



9819 
6630 



3189 



9740 
6651 



3089 



9611 
6402 



3115 14875.4 
126.5 



3209 



9583 
6458 



3125 



9114 
6402 



2712 



5 9142 
4 6458 



2684 



Energy of 



Food, 
Cals. 



6340 45239.6 
3239 30548.5 



3101 14691 . 1 
101.8 



3170 46690.1 
31327.8 



3170 15362.3 
-94.3 



15268.0 
100.00 



3115 45626.1 
30750 . 7 



3195 



15001.9 
100.00 



45570.1 
30338.1 



3195 15232.0 
-76.6 



3188 



15155.4 
100.00 



45365.9 
30548.5 



3188 14817.4 
+ 302.4 



2665 


2665 



15119.8 
100 . 00 



41900.7 
30338.1 



11562.6 
- 232 . 7 



11329.9 
100.00 



2659 41962.6 
30548.5 



2659 11414.1 
113.3 



11300.8 
100 00 



Feces, 
Cals. 



13218.1 
8171.2 



5046.9 

+ 27.2 



5074 . 1 
'34.30 

1829Q.3 

9599 . 2 



8697 . 1 
-28.9 



8668 . 2 
56.77 



17983.1 
9491.5 



8491.6 
+ 39.0 



8530 . 6 
56.86 



17751.7 
8574 . 9 



Urine 
(Cor- 
rected), 
Cals. 



2755 . 1 
1824.6 



930.5 
6.1 



936.6 
6.33 



1884.2 
1529.8 



354.4 
-4.6 



349.8 
2.29 



1633.6 
1359.6 



274.0 
+ 5.6 



9176.8 
-21.7 



9155.1 
60.41 



16562.1 
8171.2 



8390.9 

-r80.9 



8471.8 
56.03 



9926 . 4 
8574 . 9 



1351.5 
-65.8 



1285.7 
11.35 



9799 . 
8171.2 



1627.8 
-30.3 



1597.5 
14.14 



279.6 
1.86 



2084 . 7 
1795.0 



289.7 
-4.5 



285.2 
1.8S 



2237.8 
1824.6 



413.2 
+ 18.1 



431.3 
2.85 



1756.5 
1795.0 



-38.5 
-13.8 



-52.3 
-0.46 



1705.8 
1824.6 



Methane 
Cals. 



3620.2 
2722.2 



898.0 
9.1 



907.1 
6.13 



3239.9 
2560 . 7 



679.2 

-7.7 



671.5 
4.40 



3448.1 
2524 . 7 



923.4 
+ 10.4 



933.8 
6.23 



3792 . 4 
2579.4 



1213.0 
-6.5 



1206.5 
7.96 



4003.2 
2722.2 



1281.0 
+ 26.9 



1307.9 
8.65 



4004.5 
2579.4 



1425.1 
-19.8 



118.8 
-6.8 



125.6 
-1.11 



1405 . 3 
12.40 



4147.4 

2722.2 



1425.2 
- 10.1 



Metabolizable 
Energy. 



Total, 

Cals. 



25646 . 2 
17830.5 



7815.7 
59.4 



7875.1 
53.24 



23269.7 
17638.1 



5631.6 
-53.1 



5578.5 
36.54 



22561.3 
17374.9 



5186.4 
+ 71.5 



5257 . 9 
35.05 



21941.3 
17388.8 



4552 . 5 
-43.9 



4508.6 
29.75 



22562.8 
17830.5 



4732.3 
+ 176.5 



4908.8 
32.47 



26213.3 

17388.8 



8824 . 5 
-133.3 



8691.2 
76.71 



26310.4 

17830.5 



1415.1 
12.52 



8479.9 
-66.1 



8413.8 
74.45 



Per 
Grm. 
Or- 
ganic 
Mat- 
ter, 
Cals. 



2.540 



1.760 



1 411 



1.540 



3.261 



3.164 



APPENDIX. 



55 1 



TABLE II. METABOLIZABLE ENERGY OF BEET MOLASSES. 





73 

a 

'3 
< 


•6 
_o 
'C 

0) 

On 

6 
3 

6 
4 

6 

4 


Organic 
Matter 
Eaten. 


Energy of 


Apparent 

Metabolizable 

Energy. 


Feed Added. 


a 

C5 

o 


O) 

a a 
-a n 

a 


Food, 
Cals. 


Feces, 
Cals. 


Urine 
(Cor- 
rected), 
Cals. 


Methane, 
Cals. 


Total, 
Cals. 


Per 
Gram 
Or- 
ganic 
Mat- 
ter, 
Cals. 


Beet mol'ses 1 ■) 


F 
F 

H 
H 

J 
J 


8262 
6630 


1702 37946.2 
31327.8 


11365.8 
9599 . 2 


1786.1 
1530.0 


2397.9 
2560.7 


22396.4 
17637.9 




Difference .... 
Correction .... 


1632 

8110 
6402 


1702 

1611 



6618.4 
+ 330.8 


1766.6 
+ 101.3 


256.1 
+ 16.2 


-162.8 
+ 27.0 


4758.5 
+ 186.3 




Percentage . . . 
Beet mol'ses II \ 


6949 . 2 
100.00 

37544.4 
30338.1 


1867.9 
26.87 

9070.0 
8574.9 


272.3 
39.2 

2035 . 2 
1795.0 


-135.8 
-1.95 

3458.8 
2579 . 4 


4944.8 
71.16 

22980.4 
17388.8 


2.905 


Difference. . . . 
Correction.. . . 


1708 

8104 
6458 


1611 

1595 




7206.3 
-459.4 


495.1 
- 129 . 8 


240.2 
-27.2 


879.4 
-39.1 


5591.6 
-263.3 




Percentage . . . 
Beet mol'ses II \ 


6746.9 
100.00 

37461 . 1 
30548.5 


365.3 
5.40 

9198.7 
8171.2 


213.0 
3.16 

2017.2 
1824.6 


840.3 
12.44 

3422.7 
2722.2 


5328.3 
79.00 

22822.5 
17830.5 


3.308 


Difference .... 
Correction. . . . 


1646 


1595 


6912.6 
-234.3 


1027.5 
-62.7 


192.6 
-14.0 


700.5 
-20.9 


4992.0 
—136.7 




Percentage . . . 


6678.3 
100.00 


964.8 
14.45 


178.6 
2.67 


679.6 
10.18 


4855.3 
72.70 


3.044 



552 



APPENDIX. 



TABLE III. METABOLIZABLE ENERGY OF STARCH. 
EXPERIMENTS. 



kuhn's 



Feed Added. 



Starch I . 



Difference. . 
Correction. . 



Percentage . 

Starch I . . . | 

Difference . 
Correction . 

Percentage 

Starch II ... -j 

Difference . 
Correction. 

Percentage . 

Starch II.. . -j 

Difference . 
Correction. 

Percentage 

Starch II ... -j 

Difference . 
Correction. . 

Percentage . 

Starch II... -j 

Difference. . 
Correction . . 

Percentage 



2 
la A 6 



8839 

732S 



Organic 
Matter 
Eaten. 



1511 



8787 
7074 



1 = 



Energy of 



Food, 
Cals. 



1651 140964. 5 
34603.2 



1651 



160S 




1713 



8767 
7199 



1568 



8792 
7199 



1608 



1621 


1621 



1663 




1593 



8861 
7125 



1736 



9953 
7125 



6361.3 
+ 658.0 



7019.3 
100.00 



40725 . 6 
33405 . 1 



7320.5 
-492.0 



6828.5 
100.00 



40827 . 5 
34211.5 



Feces 
Cals. 



16615.5 
15505.1 



1110.4 
+ 294.8 



1405 . 2 
20.02 



17202.1 
15250.6 



1951.5 
-224.6 



1726.9 
25.29 



15804.1 
15312.2 



Urine* 
(Cor- 
rected), 
Cals. 



Methane 
Cals. 



1430.3 
1549.6 



-119.3 

+ 29.5 



-89.8 
-1.29 



1434.9 
1481.5 



-46.6 
-21.8 



-68.4 
-1.01 



1618.3 
1559.3 



6616.0 
+ 255.0 



6871.0 
100.00 



40917.4 
34211.5 



1663 



1669 




2828 



1669 



2788 




2788 



6705 . 9 
+ 334 . 1 



7040.0 
100.00 



41245.9 
33855 . 4 



7390 . 5 
-320.9 



7269.6 
100.00 



45859.6 
33855.4 



12004.2 
-193.4 



11810.8 
100.00 



491.9 
+ 114.2 



606.1 
8.82 



16270.0 
15312.2 



957.8 
+ 149.5 



1107.3 
15.73 



15485.9 
13765.2 



1720.7 
-130.5 



1590.2 
22.49 



16091.4 
13765.2 



2326 . 2 
-78.6 



2247.6 
19.03 



59.0 
+ 11.6 



70.6 
1.03 



1524.8 
1559 . 3 



-34.5 

+ 15.2 



-19.3 
-0.27 



1569.6 
1737.9 



3225 . 3 
2670.1 



655.2 
+ 50.8 



706.0 
10.06 



Apparent 

Metabolizable 

Energy. 



Total, 
Cals. 



19593.4 
14878.4 



4715.0 
282.9 



4997.9 
71.21 



3348.0 18740.6 
2491.3 14181.7 



856.7 
-36.7 



820.0 
12.01 



3021 . 1 
2268 . 5 



752.6 
+ 16.9 



769.5 
11.20 



2941.0 
2268.5 



672.5 

+ 22.2 



694.7 
9.86 



3130.5 
2480 . 6 



-168.3 
-16.5 



-184.8 
-2.61 



1643.9 
1737.9 



-94.0 
-9.9 



103.9 
-0.88 



649.9 
- 23 . 5 



626.4 



3897.8 
2480.6 



1417.2 
-14.2 



1403.0 
11.87 



4558.9 
- 208 . 9 



4350.0 
63.71 

20384.0 
15071.5 



5312.5 
+ 112.3 



5424 . 8 
78.95 



20181.6 
15071.5 



5110.1 
+ 147.2 



5257 . 3 
74.68 



21059.9 
15871.7 



5188.2 
-150.4 



5037 . 8 
71.26 



24226.5 
15871.7 



8354 . 8 
-90.7 



Per 

Grm. 
Or- 
ganic 
Mat- 
ter, 
Cals. 



3.029 



2.705 



3.347 



3.161 



3.018 



8264 . 1 
69.98 



2.964 



* Computed from carbon content. 



APPENDIX. 



553 



TABLE IV. METABOLIZABLE ENERGY OP STARCH. KELLNER's 
EXPERIMENTS. 





"3 

a 

< 

B 
B 

C 

C 

D 
D 

F 
F 

G 
G 

H 
H 

J 
J 


13 
Ph 

2 

4 

2 
1 

2 
1 

4 
3 

4 
3 

3 

4 

3 
4 


Organic 
Matter 
Eaten. 


Energy of 


Apparent 

Metabolizable 

Energy. 


Feed Added. 


S 

O 

"3 
-*> 
o 
H 


T3 B 

■vO 

T3 - 


Food, 
Cals. 


Feces, 
Cals. 


Urine 
(Cor- 
rected), 
Cals. 


Methane, 
Cals. 


Total, 
Cals. 


Per 
Grm. 
Or- 
ganic 
Mat- 
ter, 
Cais. 


Starch I and J 
II 1 


11698 
10067 


3231 
1607 


52928.6 
46129.1 


15915.8 
11874.4 


1740.1 
1958.5 


3382.7 
3716.3 


31890.0 
28579 . 9 




Difference . . 
Correction . . 


1631 

11980 
10407 


1624 

3193 
1602 


6799.5 
-30.9 


4041.4 
-8.0 


-218.4 
-1.3 


-333.6 
-2.5 


3310.1 
-19.1 




Percentage . . 

Starch I and f 
II 1 


6768.6 
100 . 00 

54016.5 
47458.0 


4033.4 
59.60 

19185.6 
15746.8 


-219.7 
-3.25 

1723.7 
1785.7 


-336.1 
-4.97 

3250 . 6 
3255.9 


3291.0 
48.62 

29856.6 
26669.6 


2.027 


Difference . . 
Correction . . 


1573 

11636 
9974 


1591 

1583 



6558.5 
+ 70.8 


3438.8 
+ 23.5 


-62.0 

+ 2.7 


-5.3 

+ 4.9 


3187.0 
+ 39.7 




Percentage . . 
Starch III . . \ 


6629 . 3 
100.00 

53902.2 
46945.4 


3462.3 
52.22 

17817.9 
15718.3 


-59.3 
-0.89 

2211.2 
2407.0 


-0.4 
-0.01 

3381.4 
2957,0 


3226 . 7 
48.68 

30491.7 
25863.1 


2.028 


Difference . . 
Correction . . 


1662 

8374 
6630 


1583 

1687 



6956.8 
-379.5 


2099.6 
-127.1 


-195.8 
-19.5 


424 . 4 
-23.9 


4628.6 
-209.0 




Percentage . . 
Starch III . . j 


6577 . 3 
100.00 

38608 . 3 
31327.8 


1972.5 
29.99 

10833.9 
9599.2 


-215.3 
-3.27 

1594.3 
1530.0 


400.5 
6.08 

3382 . 7 
2560 . 7 


4419.6 
67.20 

22797.4 
17637.9 


2.792 


Difference . . 
Correction . . 


1744 

8380 
6651 


1687 

1676 



7280.5 
-268.3 


1234.7 
-82.5 


64.3 
-13.2 


822.0 
-22.0 


5159.5 
-150.6 




Percentage . . 
Starch III . . -j 


7012.2 
100.00 

37963.6 
30750.7 


1152.2 
16.42 

10497.1 
9491.5 


51.1 
0.73 

1394.7 
1359.6 


800.0 
11.41 

3170.5 
2524 . 7 


5008.9 
71.44 

22901.3 
17374.9 


2.969 


Difference . . 
Correction . . . 


1729 

8373 
6402 


1676 

2013 



7212.9 
- 246 . 2 


1005.6 
-76.0 


35.1 
-10.9 


645.8 
-20.2 


5526.4 
-139.1 




Percentage . . 
Starch IV. . . j 


6966.7 
100 . 00 

38562.4 
30338 . 1 


929.6 
13.35 

9843.8 
8574.9 


24.2 
0.35 

1588.4 
1795.0 


625.6 
8.98 

3183.9 
2579.4 


5387.3 
77.32 

23946 . 3 
17388.8 


3.214 


Difference . . 
Correction . . 


1971 

8004 
6458 


2013 

1600 



8224 . 3 
+ 193.2 


1268.9 
+ 54.6 


-206.6 
+ 11.4 


604.5 
+ 16.4 


6557.5 
+ 110.8 




Percentage . . 
Starch IV... j 


8417.5 
100.00 

36982.6 
30548 . 5 


1323.5 
* 15.72 

9096.8 
8171.2 


-195.2 
-2.32 

1885.4 
1824.6 


620.9 
7.38 

3492 . 1 
2722.2 


6668.3 
79.22 

22508.3 
17830.5 


3.313 


Difference . . 
Correction . . 


1546 


1600 


6434 . 1 
+ 254.1 


925.6 
+ 68.0 


60.8 
+ 15.2 


769.9 
+ 22.6 


4677.8' 
+ 148.3 




Percentage . . 


6688 . 2 
100.00 


993.6 
14.85 


76.0 
1.14 


792.5 
11.85 


4826 . 1 
72.16 


3.017 



554 



APPENDIX. 



TABLE V. METABOLIZABLE ENERGY OF WHEAT GLUTEN. 



Feed Added. 



Wheat gluten -] 

Difference . . . 
Correction. 



Percentage . 

Wheat gluten 

Difference. . 
Correction. . 



Percentage 



Wheat gluten - 

Difference. . . 
Correction . . . 



Percentage . 

Wheat gluten 
I 

Difference . 
Correction . 



Percentage . . 

Wheat gluten J 
I I 

Difference . . 
Correction . 



Percentage . . 

Wheat gluten 1 
II 1 

Difference . 
Correction . 



Percentage . . 

W heat gluten j 
II 1 

Difference . . 
Correction . . 



Percentage . . 



Organic 
Matter 
Eaten. 



9311 

ss39 



^ 4) 



472 



10037 
8839 



1198 



9483 

8787 



696 



11636 
10067 



1569 



11533 

10067 



576 




576 



1157 




1157 



Energy of 



Food, 
Cals. 



Urine 
Feces, (Cor- 
Cals. rected), 

Cals. 



44025 . 3 
40964 . 5 



3060.8 
+ 502 . 9 



3563 . 7 
100.00 



48293 . 6 
40964 . 5 



7329.1 
-171.2 



7157.9 
100.00 



582 44860.3 16845.6 
0:40725.6 17202.1 



16041.5 
16615.5 



-574.0 
+ 204.0 



-370.0 
-10.38 



16593.3 
16615.5 



-22.2 
-69.4 



91.6 

-1.28 



582| 4134.7 
534.4 



3600.3 
100.00 



1746 54939 . 3 
261 146129.1 



1485 



1742 
261 



1466 



11994 
10407 



1587 



1746 
261 



1485 



8810.2 
- 380 . 5 



8429 . 7 
100.00 



54469 . 
46129.1 



8339 . 9 
+ 62.3 



8402 . 2 
100.00 



56293.6 
47458.0 



11578 1407 
99741 



8835.6 
-411.4 



8424 . 2 
100.00 



56053.6 



- 356 . 5 
-225.7 



■582.2 
-16.17 



14514.7 
11874.4 



2048 . 8* 
1430.3* 



618.5 
+ 17.6 



636.1 
17.85 



2990 . 4* 
1430 . 3* 



Methane 
Cals. 



3669 . 6 
3325 . 3 



344 . 3 

+ 40.8 



Apparent 

Metabolizable 

Energy. 



Total, 
Cals. 



22265.4 
19593.4 



2672 . 
+ 240.5 



1560.1 
-6.0 



1554 . 1 
21.71 



2036.3* 
1434.9* 



601.4 
-18.8 



2640.3 
-97.9 



2542.4 
30.16 



13753.4 
11874.4 



1879.0 
+ 16.0 



1895.0 
22.55 



17643.2 
15746.8 



1896.4 
-136.5 



1759.9 
20.89 



17322.9 



■16915.4 115718.3 



9108.2 I 1604.6 



- 934 . 1 



8174.1 
100 . 00 



-312.7 



1291.9 
15.80 



582.6 
16.18 



3372.3 
1958.5 



1413.8 
-16.2 



1397.6 
16.58 



3092 . 1 
1958.5 



1133.6 
+ 2.6 



1136 
13.52 



2744 . 1 

1785.7 



385.1 
10.81 



3703.0 
3325 . 3 



2912.5 
81.72 



25006 . 9 
19593.4 



377.7 
-13.9 



363.8 
5.08 



3346.7 
3348.0 



-1.3 
■43.9 



-45.2 
-1.26 



3753.7 
3716.3 



37.4 
■30.7 



6.7 

0.08 



3574.9 
3716.3 



141.4 
+ 5.0 



136.4 
-1.62 



5413.5 
-81.9 



Per 
Gnn. 
Or- 
ganic 
Mat- 
ter, 
Cals. 



5.057 



5331.6 
74.49 



22631.7 
18740.6 



4.608 



3891.1 
-246.0 



3645 . 1 
101.25 



33298.6 
28579.9 



6.263 



4718.7 
- 235 . 7 



4483.0 
53.18 



34048.6 
28579.9 



5468.7 
+ 38.7 



5507.4 
65.55 



958.4 
-15.5 



942.9 
11.19 



3468.0 
2407.0 



1Q61.0 
-47.9 



1013.1 
12.39 



2973.0 32933.3 
3255.9 26669.6 



- 282 . 9 
-28.2 



-311.1 
-3.69 



3171.9 
2957.0 



214.9 
-58.8 



156.1 
1.91 



6263.7 
-231.2 



6032 . 5 
71.61 



32090.8 
25863 . 1 



6227.7 
-514.7 



3.019 



3.719 



4.062 



5713.0 
69.90 



4.061 



* Estimated from carbon content. 



APPENDIX. 



555 



TABLE VI. 


METABOLIZABLE 


ENERGY OF PEANUT 


OIL. 






"3 
S 

1 


.2 
P-< 


Organic 
Matter 
Eaten. 


Energy of 


Apparent 

Metabolizable 

Energy. 


Feed Added. 


a 

o 

o 
H 


T3 

CO 

5 

. en 
qj a 

■So 

«! 

c 


Food, 
Cals. 


Feces, 

Cals. 


Urine 
(Cor- 
rected), 
Cals. 


Methane, 
Cals. 


Total, 
Cals. 


Per 

Gram 
Or- 
ganic 
Mat- 
ter, 
Cals. 


Peanut oil I. . i 


D 
D 

F 
F 

G 
G 


3 

1 

5 
3 

5 
3 


10752 
9974 


709 

■ 


54007.3 
46945.4 


1749.2 
15718.3 


2351.2 
2407.0 


2909.0 
2957.0 


31279.6 
25863 . 1 




Difference . . . 
Correction.. . 


778 

7491 
6630 


709 

798 



7061.9 
-331.1 


1749.2 
-110.9 


-55.8 
-17.0 


-48.0 
-20.8 


5416.5 
-182.4 




Percentage . . 
Peanut oil II . \ 


6730.8 
100.00 

39185.9 
31327.8 


1638.3 
24.34 

14585.7 
9599 . 2 


-72.8 
-1.08 

1455.0 
1530.0 


-68.8 
-1.02 

1369 . 1 

2560 . 7 


5234 . 1 

-77.76 

21776.1 
17637.9 


7.382 


Difference . . . 
Correction. . . 


861 

7396 
6651 


798 

798 



7858.1 
-302.0 


4986 . 5 
-92.5 


-75.0 
-14.8 


-1191.6 
-24.7 


4138.2 
-170.0 




Percentage . . 
Peanut oil II. -j 


7556.1 
100.00 

38057.3 
30750.7 


4894.0 
64.77 

12512.9 
9491.5 


-89.8 
-1.19 

1452.1 
1359.6 


1216.3 
-16.10 

2371.2 
2524 . 7 


3968.2 
52.52 

21721.1 
17374.9 


4.973 


Difference. . . 
Correction. . . 


745 


798 


7306 . 6 
+ 249.5 


3021.4 
+ 77.0 


92.5 
+ 11.0 


-153.5 

+ 20.5 


4346 . 2 
+ 141.0 




Percentage . . 


7556 . 1 
100.00 


3098.4 
41.00 


103.5 
1.37 


-133.0 
-1.76 


4487 . 2 
59.39 


5.623 



556 



APPENDIX. 











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© © 


_o 


rH CO 


<M CO 


(M <# 










,_: 








a 


Ph En 


o o 


X X 


'3 
•3 












m 










M 










M 














<D 








CO 








0) 












+3 








+3 

-f3 








r; -1-9 












6 -^ : 
o "3 






d -d 






£ ■& : 








> 


"S £ : 




If | : 




I'm g : 








.. + £ w 




•. + M m ; 




O , — ( 

^ "l" tH rH 








£ d £ H d j 


^d£ £ d i 

g>-2 d d .2 e 


g»l d d -2 S 
te^-2 .2 | £ 

1 1 a s | q 

^ 03 O O 03 

S«o O ffl 




s».2 a d -2 p 




e +1 o o +» a 
&5 gn3 •-§ g & 




^ TO &_, (H TO JC 


lis £ ! p 




* 










^ 










^ 













APPENDIX. 



557 



1 as 
































' 


nta 

iza 

of 

es.s 




OS ■<* 


Tf( 00 1-1 GO 






00 CO N1 


CO CO 


g^-SW 




iO ^ 


lO CO t M 


ft 














CM CO 


OS (M 


i-t CN 


c 


CO t-h NCN 


iO CO O 


•O OS CD CM 


00 1> 'i-H ' 


MO 


CM CS 1 


»o CO 


1— 


fflH NO) 


00 O 


n 


(N CM lOS OS 


00 CO 


CM 


a £A 
Wo 
O 


•"# t> 


t^rj- 


i-H C 


1 — 


1— 1 CO TfH -* 


OS CD 


c: 


00 CM lO i-H 


N 1-H 


CO 




iO if. 


T-H^C 

co"cn 


1— 
' -t 


10 


10 


Os^CN 






O^H 


i-H^O 

th"cm" 


i-H 

cm" 




























Excess 
ver Main- 
tenance, 
Cals. 


TJH TfH 


»o 


10 1> 


oc 


CO TP 


N- 00 Os 00 ' — 


CO rH 


10 >o 


O Tt< 


CO 


CO OS 


■* c 


TjH O 


■t 


co os 


10 co 1—1 co lie 


CM CO 


OS CD 


CO l> 


00 


1-1 


00 CN 


Off 


c 


<N »0 


00 os as 1— 1 'r-^. 


co 10 


N N 


10 N 


1> 


^h" 1 


OS 


OS « 

rn"o: 


If. 

OC 




°i | ^ co a 


1 ' 


OS CM 


CM CO 

o"^~ 


"3* 

10" 


O 


T— 1 


i-H 


M 




* —l 


1—1 i-H 






i-H 




~G 


co 






OS t~- 


O iO 


O . <L> 












mput 
Vlain- 
snanc 
Cals. 


OS 







os co 


. I> 


O 


oc 






CO CO 


°V 







"^ l °- 


CN^ O^ 


o~£ 


T)T 


co 




co" co 


co" cm" 


O 


7—1 






i-H 1-H 


i-H i-H 


, 


O T* 


O 


oc 


oc 


<M T* 


CO id 




CO i-H 


lo as co 


_o,2 ^ • 


CO OS 


co 


QC 


-t 


CD OS 


to 


»c 


OS CO 


CO I> 


00 




OS 


OC 


c 


t« >0 


O CO 


1> 


CO iO 


rH CO 


N 


-^ 03 Oj c3 

5.S co 


O ^H 


°°~. 


co 


LC 


1:0 + 


t>^ oq_ 


OC 


CM 1 


CM^ co_ 


"i 


S — H 


O | 


>o" 


1^ 


QC 


»o 


10" t>-" 


l> 


co" 


co" t> 


io" 




<N 


IM 


i— 




CM 


CM i-H 




CM 


CM i-H 




© jj 


O 







IO t-H 


N lO 




CO 


oc 




00 10 


IO CO 




co 


CO 




CM CO 


i-H OS 


t^ 


cc 




CO CO 


'CD iO 


■6 















t^ 


■* 




ca rt< 


CM CO 














"o3 












s 


w 


tc 




>-s 1-5 


pc, fe 


























u 










S-H 














05 








05 








0) 


















-♦^ 








-^ 




















•+J 








•+^ 












"cS += 








co I,' 

S S : 






l i ; 










) 






bX) 






bD 








> 


u "a 

'S * 

** a. 
fen 0. 






> 


.2 - S 

bJO 05 




fe : -S "53" 

^3 ^b g 








rC C 






Ab >> 




03 Sh > 








•. O S 






-. a 




+ s ? ; 








^d«2 £ 


c 


0. 


^ c <2 .2 co. 


.. ««2 -2 g o5 




L? "S O C 


.c 


e 


k? -s O 15 0. 


j~h.2 d d ■« d 




'-£ 


a. 


^ Co »ih .^h ?s ^ 




S h+> -t= 


05 


E- 






t- 


0. 


5 C5 O _ s*h 

g'-s 05 as rs fS 

s w l u ra JT 

1% 05 E C "5 Q 
t<! cj O O o3 




3 "5 05 0. 

n « L Lh 

-§ S3 s e 

§ e3 C 


"5 

cc 


St 
P 


S r2 05 <u r2 S 

-2 co S C Jg P 
g 08 O ' =* 




§mo 


pq 




•«pqo PQ 




* 










^ 










O 













558 



APPENDIX. 



M 



Pl. 



oo o 



W*og° 
o 



coco 



cot> 

MS t» 



TJH |> 


t~<N 


I>CO 

t>- oo 

to i-i 

<N 1 


O CO 

OS o 



00 CN 

OS OS 



o o 
os 35 

"OH 



O CO 



oo 
•t o 

■*, °i 

co'ci 



8'3 S • 



3d g 



cja 



t^iO 


IN OS 


<N ^H 


TjH (N 


ON 


b- CO 


M -.+ 


W - 1 


OS 


OS 



CO 



MO WN 



i-t co 

i-H «0 

coo. 

Os""* 



lO l> 00 OS 

IN CO OS CO 



i-H IC 


CO o 


CO 00 


CO l> 

CO^H 

OS~ + 


CO 00 

«H 00 

U5 IN 

OS" 1 


iO CO 

CN l-H 

CN CO 






ONlm 
>o _|_ CO_ 



or 


00 


<N CO 


(/ 


o 


CO N 


co 


lO 


OH 


t^ 


TJH 


sa + 






O 



c 



W 



K 



3 <- 



^0 53 



: PQO O 



I § 

- o 

— «s 

PQ 



.J3 M 
to b 

o 

+ h 

>"~l =*"! 

2 .2 

s +' o 

38 -a s 

■s»G 



,0 
bfi 



,J3 
bfi 



* B 
+3 be 

+ ° 

; g «s 

-.2 c 



d cu 



c 
O 



■a S 

cd yr 

pq 



^•a s 

B 2 H 



o 
O 



a> 

•2 § 

"S £ 

-a ss 

S3 rsj 

to Q 

pq 



APPENDIX. 



559 



c 




































OS CO 




-HH CO 


rH 


us 


ercen 
Utili 
tion 
Exce 


00 r- 




CM 'oO 


CO 


00 


lO CO 




lO »C 


■* 


>o 


Cm 












. ^-o 


rH lO 


CO ■<* 


O CM 00 


CO CO 


o^t< 


TJH CO 


oc 


00 CO 


rH CM 


co r^ 


CO 


Energy 

of Gain 

orrecte 

Cals. 


co co 


OS OS 


OS CO lO 


t- •* 


co r^ 


OO 


o. 


o o 


rH OS 


O CC 


CO 


t*- i> 


os ■* 


^* O |Tf 


rH CO 


00 C 


OS CO 


CM 


CO 00 


-CH CO 




OS 


CO 1 


lOCM 


oqojcc 


° 1 


OS CM 


rH~°! 


o 




IQ CO 


OSC 


. °°^ 


t~" ' 


t-" + 


t-"cM"iCj 


- •* 1 


CO"-r 


wcm" 


*t 


^"+ 


■*"CN 


cm" 


O 
















































a . 


00 co >o t* 


OS b- 


<M 


o ^ 


OS I> 


CO 00 


|oc 


rtn co r~->o 


CM Tf 


00 


tn*3 0) 

»S a .3 


om nco 


OOS 


r-, 


■^ CO 


•* ir. 


O CO 


c^: 


OS CD 


iC CO 


CM 1> 


■<cH 


O CO CO CM 


OS OS 


OS 


O CO 


coo: 


CO -^-i 




t^OO 


CO >0 


CM J> 


rh 


8*5(3 


oo i-i ,co ■* 


CS_CC 

cm"co" 


CO 

oc 


-* 1 
CM 


co^co t>^co 
cm"+ cm"^" 


a 


lO_rH 

oo" + 


t> CO 

oo" + 


CD^CC 
oTrt 


__ OS^ 

" ■* 


o~ 


rH rH 

1 


'" H 




'~ H 


y—l 


' —1 












•2 s »,- . 

Sj2 «o 


lO H 


■* 


t» 


O ic 




CM OS 


OS 


CO 


t>- c 




rH 00 


o 


I© 


rH CC 

oq_ cr 


" 


oS d^ 


tjT co" 


co" 


co" 


co" c\ 




O 


I— 1 1— 1 


■^ 


1—1 


T-i r- 






coco 


O 00 


CM 


■*& rH 


CO 


>o 


oc 


Tfl CO 


1> o 


oo 


etabo 
izable 
nergy 
Cals. 


CO CO 


d oo 


,_l 


o'co 


"# 


o 


CO CO CO 


CM t> 


-CH 


T-H CO 


oo oo 


OS 


rH CO 


■* 


CO 




OS 00 


oo cc 


Th 


<N rH 


O CO 


CC 


CO 1 


CM^ 


00 


t 


tV ?.'" H 


iO_ CC 


. °i. 


SB-H 


CO" I 


co" r-' 


X. 


co" 


co" 


r-" 


oc 


cm" + 


cm" i> 


" •*" 


CM 


CM rH 




CM 


CM 


1—t 




CM 


CM r- 




rage 

ve 

ght, 

SB. 


lO OS 


CM 


1-* 


CO IT. 














os oo 


CO 


>o 


CD CC 






OS CO 


CO 


CO 


lO CT 




CO CO 


CO 


CO 


CO ir: 




T3 














IQ Tt* 


to 


Tt< 


CO CC 




0) 

Ph 












"3 












Anim 


w w 


i-s 


HS 


^ ft 


















M 










tl 










M 














CD 








CD 








CD 












-u 


























(id -J 




&h"o3 += 








0? +J 








13 S ,C 

a m : 
fe.8 '£ 




I 6 -g 

5 fi £ 


o ; 




CO fl ^3 
CD c he 
co. cd a) 

^2 ^ 








£03 




F 3 =3 






o s 








-Es gp ^ : 










Itf ^ 








1X2 o a 




, o ;= 






o a 








•+H IH 




"+H r- 






+ r- tn 








s fl £ a c 4 


3 _ o c 


ri 3- 


• - ° o 

• C =*H (4-, P 


s 




1.2 a a .2 £ 


■fc-2 a e 


.2 ^T 


00 O _i C 


g 




^.2 .2 15 £ 


cq -g .2 S 


« £ 


S^o o -t 

2 TO •« •-( 05 


CD 
(-1 




■x, fn -^ -r> ^ a 


g =§ o c 


ph a 


8 h* 1 -^ f- 


CD 




H w E S 2 P 

F» os o O co 

~fflO O ffl 


03 


lSTj 4) CD rs 
^ CO C g V 

oj o O °5 


S3 

s 




pq 


|ao o pc 




I 


fc) 










Bq 










cq 













560 



APPENDIX. 



35 — a o 



CO CO 
00 iC 



Woo 
o 



<N rH 


rHCO 


1> CM 


CO >C 
<0> IQ 
<M rH 


rH 00 

o -* 

rH CO 


OS CO 

r* o 
cO~c>f 



CD CO OS O 
t^ <M OS CO 

COCO CO^CN 



OS <N 


rH O 


rH TjH 


O CO 

t^rH 

OS rH 

co"+ 


l> CO 

oo co 

O rH 


CO th 
to CO 



a . 

m « o • 
<t>S 2.3 



rH CO HftONM 



OS CO 
OS CO 
CO (N 



CO rH 00 OS 00 
Mffl NO « 
HiO NCO M 



00*" I 00 + 00 CO , >o 



coi> 


CO to 


rH 00 


CO 


rH CO 


r* t~- 


(M CO 


>~ 


OS CO 


tO rH 


t^ rH 


'O 


CO rH 


»o CO 


rH CO 


/ 


oo" I 


oo" + 


oTtjh" 


-r 



o »o 



00 o 

OS *# 
CO <N 

00" + 



to co 



CO CO 

co •* 

CO CO 

oo + 



(N OS 

00 CO 
OS o 



ft.5 Cm 

tj is 

oS fl 

o 



o » >> . 

J^ c3 a> c3 



o co 

00 CO 
OS CM 



CN CO 
<M CO 

00 rH 



■>* tO 

»o o 

CO -rJH 

<n + 

CN 



i>rJ ^W 



X 



X 



« fl 



+ 

.2 a 



cd o 

:fflO 



CQ 



o a 



s=! S 



-, sn 



pq 



a 3 £ 

Qj rH 

CO -, 

03 -2 

OS g 
O c3 

as? 



:fflo 



fiq 






o PQ 








C 




8 





a 






o 


3 


H 


+3 


03 


" 


O 


cr 


e3 




~c- 


PUO 








t= 







fl s 



r, SO 



X 



APPENDIX. 



56i 



o+- O « 
Oh 



wss s 



MO CO"* 



00 o 

rH CO 

«o + 



"tf 


^ t> 


co 

<N ^ 

co~ 


CO iH 
CO rH 
00 I> 



00 rH 



CO <M 

io co 

O CO 

00" I 



^H IC 

CM CO 



a os * 
o 



co co 



co co 
i> co 

©"* + 



H 03 

OCD 
■* O 



IN O 


<N CM 


-* co 


t> CO 
to rf 
CO CM 
l>~ 1 




(M b- 

co 00 
t^co" 



o b- 



rH lO 
CO CO 

»o CM 

co~ I 



iO CO 
© CO 

CM rH 



C35 CO 

<M TJH 

r-H CO 



6 s 



■S3 s>,3 

<u.2 BO 



CO rH 
O 00 
© I 



t> 


1-1 CO 


CO rH 


CO <M 




CM 1 


<M 



00 lO 

OS co 

CM^<M 

co" I 






> 



PC 



pq 



, o 



a£ 
.2 a 
S.J 



i a 8 

IfflO 



o 



PQ 



a w 

ra b< 

be e 



■• rt«S 

s.2d 

£ g'-s 

Oh g 
TO &h 

^PQO 



rH jfcj 

as g 

n 



a o 

o>-a 

+i H 
p S3 

■?„ W 

bC u 

•. a<2 

s.2 a 

-2 S'-g 

o~ g 

s 2 S 



fe 



-a 

ho 



1 § 

03 t-, 



562 



APPENDIX. 



CJ 



9 

Ml , 








CN 


b. 








i-H 


<M 








© 


CO 


' 


ercen 

Utili 
tion 
Exce 


-* a 


«* co 


ic r^- 


«3 T}1 


«5 <* 


io co 


Ph 








Energy 
of Gain 
orrected), 
Cals. 


OOO 

O »H 


00 CO 

th b- 


IC t- 


oc 


b-»C 


^H kO 

CN © 


© © 
«H 00 


© 


00 t^ 

cot- 


T-H 00 

© t> 


© IO 

CO —1 


CN 


© <N 


T-H © 


O CO 


c: 


© CN 


l> 00 


© iC 


3 


oo oo 


© IO 


iO CN 


co 


00 


CO rH 


UJ^N 


o 


U^iH 


Tt< **1 


©,co 


© 


© CN 


I> 00 


©_iO^ 




00" 1 


oo"io" 


CN 


©" 1 


©"+ 


©"r-' 


O) 


oo" 1 


t-" + 


oo"©" 


cn" 


o 


























w 


























.9 m 


CO t» 


CO© 


TJH O 


-r 


O CN 


OO 00 


© rH 


• r 


co r- 


© co 


CN CN 


© 


m'S § gj 


<N 00 


T-H b- 


co co 


I- 


1—1 i-H 


© Tfl 


■* (M 


Cl 


CO Tfl 


00 T« 


co © 


co 




i-H CO 


>o © 


IO Th 


~ 


CO CO 


(M © 


co © 


cc 


tO 1-H 


co co 


t> © 


i-H 


co _l 


CO i-i 


H CO 


«c 


© CN 


t^ © 


CO_© 


c: 


COlO 


°°.."3. 


eo^© 


l>^ 


o 


co* 


CO 1 


CO*"©" 


'C 


oo" 1 


oo" + 


©"co" 


© 


©" 1 


m i-h" 


1>"t-h" 


»o" 


1-1 




1-H i-H 




?-H 


7-1 


i-H t-H 




r ~' 


^ + 


i-H i-H 










# 


omputed 
Mainte- 
nance, 
Cals. 


o as 


co »o 


tN © 


CD CO 


CN b- 


l> (M 


CO CO 


r- © 


CO © 


b- ©^ 


Cft © 


J> (N^ 


t>r t>r 


co" co" 


io" ^ 


O 


i— 1 i-H 


i— 1 i—l 


1-H i-H 




CO b- 


CO © 


-r 


CO (M 


T-H © 


w. 


00 r- 


i-H 1-4 


© 


oaf,. 

£>-£ Mm 
e3-3 ^^ 


00 00 


t- © 


1^ 


COt-h 


CN © 


o 


© T« 


© CO 


co 


■* CO 


00 b- 


c 


co co 


© © 


re 


© i-H 


r- © 




J2 C3 oj 55 


°-+ 


o_ »c 


>S 


OSN 


l> ©^ 


C 


O^iO 


»o °° 


t> 


s-w 


TfH 


t)T oo" 


ic 


N I 


of ©" 


CC 


c^" 1 


t-T ic" 


io" 


CO 


CO (N 




co 


co e^ 




CO 


CO <N 






CN CO 


t- © 


r-H CO 


i-I (M 


t>. CO 


00 ■* 




CO t> 


co © 


© 00 


CO CO 


© © 


l> © 


•d 








.2 


CO ■* 


CO i-l 


TH 1-H 


Ph 








"3 








1 


ffl PQ 


D O 


Q Q 


(3 












M 










u 










u 














45 








4> 








4) 












-+^ 








+s 








-^> 












+» 




























o3 .*» 






o3 -£ 






03 +3 










° bD 






s -a : 






a -a : 








d o "S 




ci o "33 




C 2 








-Sd * : 




5 1 * : 




Sf I* : 








.3 8, g 




-3 S) g 




^S) g 

be «-r > 








be £r > 




bo vT > 










oa ; 




o a ; 




O a ; 








i m ^ ! 




+ sh (h ! 




n p 








•• aS £ a a 


•■• et<S <S a a 


•• d ° <£ d g 

1-2 d d • 2 d 




g.S d a .2 c 


g.2 a d .2 c 




■S *? o o -e a 


S += o o -g a 




■S? 03 •-* .-h 03 E- 


-2 S'-S '■§ S & 




~ u "S "S »h ,4) 




3^§ 8 -ai 

^ 1 S & 1 (= 

g 03 O O w 


^•3 S 1 -a!- 

S 03 O O "3 


^-ts 8 8 -a S 

S 03 o O «3 M 

<«o o PQ 




Ifflo a m 


<WO O « 




pi 










Pi 










fe 













APPENDIX. 



563 



tage 

za- 

of 

IBS. 








tr. 


c 








CM 










OS 


CM 




83 §g 


c 


c 




OS 




1-H CO 


gp'-ss 


■<t 


'C 




T}< 




xJH lO 


Ph 














. 










* 


# 














>>a"S 


•^ co 


©CM 


CM CM 


c 


t- 00 


OS OS 


00 CO 




CMt-h 


COC 


CO CO 


O 


























Inerg 
f Gai 
rrecti 
Cals. 


T)H Tf 


os r- 


CO CC 


c 


1— 1 os 


i-H CC 


00 os 




■* l> 


—1 1^ 


00 ■* 


■* 


CO i-H 


■* OS 


Itf Tf 


c 


1— 1 00 


CM IC 


i> co 




CO ■* 


i-H O: 


O CM 


00 


OS 1—1 


S-+ 


t-^CC 


>c 


s M 


CC^_i_ CO^OS 




1+ 


°14 


CO -* 


00 


Woo 




CO 


co" 


CM 


l-H 


tH 


^ \ 




-* 


■* 


-*",-<* 


cm" 


























a - 


«D OS 


lO OS 


•* 1C 


OS 


CO OS 


■* CC 


t> CO 




CO CO 


CO "C 


^h CO 


00 


Excess 

ver Ma: 

tenancy 

Cals. 


OS CM 


CM OS 


CM Tt 


l> 


b- 00 


00 CM 


O OS 




I>CM 


OS 1- 


^H CO 


■* 


CO 00 


10 co 


OS O- 


S! 


00 


t^ CC 


i-t CO 




l>i-H 


00 cc 


CM OS 


CM 


O CM 


CO CM 


iC IC 


OS 


Tf^CM 


CM iH 


Tf OS 




Tt<^H 


iO CM 


OO^CO 


■* 


co" + 


co"+ 


CO"i— 


" -f 


co" 1 


co"+ co" I 




00" + 


00" -r 


00" co" 


10" 


O 


























-a 


00 a- 




CO 





1> 


CM 


g-sS" 3 
Si3 So 


CO CC 




CO 


i-H 


CO 


lO 


CM OC 




10 


CM 





I> 


«0 CM 


v 


CM 


1-H 


°J. 


CO^ 


og c 


CO K 




10" 


<o 


i-T 







1— 1 1— 




^ 


i-H 


tH 


T-H 




•* OS 


CO TT 


a 


CO OS 


r- 


t^ 


c 


CO 


co 


10 


00 


etabo 
izable 
nergy 
Cals. 


CO CM 


cd a 


t^ 


O 00 


T-l 


i-H 


c 


Tt< CM 


CO 


,_(' 


Tt< 


os 00 


r- t-< 


c- 


Tfl O 


co 


00 


": 


00 i-H 


OS 


t^ 


CM 


lO CM 


00 OC 


. a 


t- <M 


10 


1—1 


cc 


CO i-H 


•* 





"tf 
























S-w 


Os" + 


OS" -tf 


-t 


00 I 


00 


Tin" 


-t 


0"+ 


0" 


10 


kO 


i-H 


1-H T- 




1— t 


1—1 


1— 1 




CM 


CM 


1-1 




0) - 


CO 1-1 







00 


i-H 


1-H 














OS <M 




1— 1 


cm' 


O 


CM 


< F 


-tf CC 




CO 


CM 


CM 


O 


CO CC 




CO 


CO 


CO 


CO 


■d 














.2 








rO 


e 




Ph 


IM T-t 




CM 


1-H 


CM 


i-H 














"3 


"3 














1— 1 1— 
1— 1 M 
1— 1 I— 




> 

h- 1 


> 
(— 1 


> 


> 


<J 


















t* 










Ih 










(h 














a> 








CD 








aj 




















-*^> 








+^ 












-^> 








+3 








4^ 












a += 






03 j- 








S +: 












a -a 






d rC 

w bi 


D '. 








'. 








-d » "53" 




J32 '4 






J3 










b a £ 




E S * 






§i ^ 














00 (-1 P* 






CO tH > 










O a 




O « 

1 (h t- 






a 

1 u 1+ 










C m-i t_, Z 


| 


d£ £ 


d «. 


d <*« <h 


d g 




.2 a a .£ 


B 


•2d B 


•J c 


•2d d 


.2 § 




■So O "*i 


a. 


"SO c 


"S CL 


"SO c 


"S cp 




cS •!=! -m ej 


(. 


o3 .2 .S 


CCS L. 


o3 •-; .S 


Cj (H 




f-t ,+= -t^ (_ 


a. 


(H +3 -£ 


^ a. 


1^ += += 


t- CD 




• . r3 a> ct> r; 
-si eg G C » 


fc 

£ 


_ c 
• . r3 as a. 

rfS co g E 




sal 
rrec 

rrec 


r3 * 

2 




u cj O K 




<3 O C 


c3 ^ 


y « c 


cS " 




hfflo O PC 




^«0 C 


pq 


^fflo C 


« 












J** 






&2 










CQ 










CQ 













5 6 4 



APPENDIX. 



(0 

5 So m 


Os r^ 


OS I> 




OS i-H 


ercen 
Utili: 
tion 
Exce 


rH o: 


^H CO 




OS 00 


rH »fl 


rH tO 




co -n 


ft 










Energy 

of Gain 

(Corrected), 

Cals. 


rf< lO 


OS CO 


so 


tJH t- 


1— 1 i-H 


CM CO 


OS 


1> o 


t^ o 


Oth CO 


00 kO 


COrH 


05 


r}H i-H 


CD CO 


OS "* 


-H 


o o 


O 03 


OS CO 


co 


oo co 


(M CM 


r. 


00 CD 


-h O 


-h CM 


CI 


i> CO 


i-h rr 


tO CO 


CM 


OS CO 


CO -^ 


X 


OS^ 1 
CO 


O CM 


Ol^ 


00 


Oi 1 


OS ^H 


o^o 


rH 


C0"+ 


td-T 


>.- 


^" + 


rfTi— 1 


cm" co" 


co"-f 


TtTr-T 


cm" 
























a - 


O 00 


oo co 


10 


CO CM 


00 00 


CO CO 


CO 


i— 1 r« 


l> rf 


rH CO 


00 


Excess 
ver Ma: 
tenancy 

Cals. • 


CO O 


co co 


1- 


I-H I>» 


00 rH 


co co 


1^ 


too 


"* CO 


oo o 


r^ 


to o 


"O OS 


iO 


CM rH 


CD 00 


"O OS 


IC 


i-H tO 


CO l> 


co o 


co 


<M 00 


CD <TC 


SO 


OrH 


i-H rH 


co^co 


IN 


OS i-H 


t^ co 


i— 1 i-H 


o 


<N + 


coco" 


OS 


oc"+ 


oo" + 


oo" CO 


to" oo" 1 


oo"-(- 


Os"r«" 


to" 


O 


1-1 


















| 




mputed 
ainte- 
lance, 
Cals. 


O <N 


O CM 


00 


rH 


co «o 


© to 


-# 


,_,' 


t^ r- 


co r- 


•* 


t^ 


■* 'hv 


ih cq_ 


1—1 


r-^ 


OS a 


of i-T 


Of «-T 


cm" 




o 


i— i i— ( 


1-1 '""' 


1-1 


1-1 




i — i 


















, 


© io 


■O 


CO CM 


oo to 


CO 


OS T« 


tO 


r^ 


oo 


2i] >> ■ 


OS rn' 


1> 


I-H t~- 


00 T— 1 


r^ 


cs o 


os 


,_! 


t^ 




S3 »> 


tO 


oo rH 


CM !> 


•c 


to to 


o 


i> 


co 


4J H QJ 03 

«.2 CO 


^ o 


■- 




co_ ©^ 


01 


OH 


os 


00 


o^ 


™ «5 


OS 


©" + 


o" to" 


to 


H 1 


o" 


to" 


to" 


CM i— i 




CM 


CM I-H 




CM 


CM 


1-1 






i—i i— i 


O rH 


OS 


o 


tO CI 


O CM 


r« 


r« 




co o 


rH O 


t^ 


r« 


CO CO 


CO CD 


CO 


CO 


T3 










.2 




rO 


* 




PL, 


CO H 


CM ?H 


CM 


I-H 










"3 

6 

'c 










> > 


> r> 


I-H 
> 


HH 
> 


<J 






















*H 










M 






















<u 








CD 
















































-^ 




















-^ i 






03 -+^> 






03 -u 


















s -a : 






tC 


d ; 








jd'S 




^.S 




X.H 'Z 










g £ : 




2 S * : 




s s ^ 










* g : 




5m ? 




1& ^ 












IB h >■ 












+'t : 




+s * ; 




+ s ; 










C<2 (3 a. 


a«2 .2 c i 


- o C 
=*h s£ 


<x> 




.2 a .2 .c 


•2 a o -2 fe 


•2o c 


•2 g 




"So -Sa. 


"£ O O "SO. 


■*i o c 


■H CD 




03 •-< CO b 


03 --r; .S 03 £ 


03 -rt •- 


03 ^H 




*■■ "S t* i 


tn += 43 h I 


^ ~S ■tr' 


t^ CD 




_ O , St- 

U 03 O =3 


•••a 8 g ^^= 

% 03 lh r: 03 *jr 
r-S3 oj E P to C 

JJ 03 o o <s w 


^ 03 tn Lj 
CJ 03 O o 


03 -h 
to Q 
03 W 




jsmo m 


^fQO o PQ 


cBfflO o 


pq 














02 








&Q 










£>5 













APPENDIX. 



565 






































5*^J 


OS O 


IN T* 


I-H 00 


ercen 
Utilii 
tion 
Exce 








OS CO 


■* «o 


Tfi r^ 


CO ■* 


*C CO 


10 10 


&H 








Energy 
of Gain 
orrected), 
Cals. 


OS CM 

co 


I>tH 


00-* 
"# CO 


00 


OS ■* 




10 co 

O CM 


OS r^ 
1> 10 


CM 


00 IO- 

CO rH 


CO i-H 

IO T-H 


T-H CD 

CD 00 


00 


OS CO 


10 co 


00 co 


~v 


CO tH 


«o co 


T-H CO 


'O 


T-H CM 


co 00 


T-H IQ 


10 


CM 1 


CM CM 


"* *?, 


oc 


CM 1 


(N CO 


OSl> 




00 


00 co 


CM^OO 


00 


IO" ' 


*o" + 


iO~i-T 


co' 


00" ' 


00" 1 


l>lO 


CI 


00"+ 


os"r-~ 


T^" 


O 




















































Excess 
ver Main- 
tenance, 

Cals. 


"ON 


00 co 


■* CO 


T-H 


1>T-H 


co co 


00 


c 


CO t> 


CO IO 


00 T-H 


I> 


00 


t- co 


"* 


t< 


os os 


O CO 


t^ CO 


T-H 


T( OS 


t^ tH 


00 CM 


co 


I>OS 


00 l> 


CO O 


co 


COH 


IO i-H 


CO Tti 


OS 


00 CO 


CM O 


CM O 


CM 


°°- 1 


r- *0 


co»-^ 


(M 


IO I 


IO CO 


OS CD^ 


CM 


co 


T-H l> 


OO^CD^ 


°i. 


I— 1 


r-T + 


cm"-*" 


X 




3 1 


mo" 


co' 


co" + 


co"co" 


co" 


O 


T— 1 


1—1 


T-H 




1—1 




I-H T-H 




1-1 


i-H 


T-H T-H 




13 


"H 


co os 


IO 


as . - 








omput 
Main- 

tenanc 
Cals. 


00 H 


O CO 


CM 


[> 


r}4 1> 


CM CO 


r^ CO 


CO t>. 


co os 


t> 0^ 


of i-T 


i>" t>r 


co" co" 


O 


H 1— 1 


1— 1 i-H 


1-H T-H 




IO I> 


00 b- 


rH 


Oh 


OS OS 





co i> 


CO CD 


1> 


stabo- 
izable 
nergy 
Oals. 


co 


IO t-h 


~v 


os 


os 


,_, 


CO OS 


CD OS 


CD 


CM OS 


co r- 


"CO 


OS i-H 


t^ t^ 


OS 


IO CO 


OS CD 


CM 


<M 1 


i-H 00 


cm 


00 1 


00 10 


C) 


00 1 


00 CD 


CM 


•> 














g-H 


Tfl 


T« IO 


00 


T-H 


i-i 00 


CO 


OS" 


os co 


CO 


<M 


CM T-H 




CO 


CO CM 




CM 


CM CM 






OS O 


T-H CO 


Tt< OS 








h > M be 


T-H TJH 


06 CO 


CO CO 




OS T* 


CO t- 


10 


CD CO 


CO CD 


CO CO 


•d 








_o 


CO tH 


CM -* 


CM t-h 


Ph 








"3 

S 

•a 








1— 1 1— 1 

> > 


PQ ffl 


a 


< 












u 










-H 










rH 














a 








co 








CO 












■*j 








-u 








+s 












-t-> 








+3 








-*5 












o3 -p 






03 -P 






03 -U 










O r0 

G bfl 






a -a : 














^ « "S 




-0 « '53 




-0 2 "«3 








S"| * : 




B s * : 




2 1 * : 








CO rH > 




°3 Oi O 




5 S g • 

03 (H r> 








+ 2 ^ | 




a : 

1 rH tH 




O W ; 

1 (-1 Eh 








fl «2 =2 fl a 


o£ 2 a 


° «2 c^ 




.2 a a .2 £ 


.2 .2 % 


.2 a .2 § 




-go g a 


-go go. 


go g co 




03 -rj --H 03 (- 


TO 'rH >H TO J- 


C3 *f-H ..-» 03 Ph 




rH -g -+s s-i a. 


(h +s -p (h a 


»h +=■ -p sh as 




O s*= 

• •■^ cu r3 rE 
his 2 G G »P 


• . rg a» as r3 q - 

TO tL EL TO "JT 

"•? S G G 2C 


••'3 co co "3 S 
to t_i r_i to jr 

Hg Og S g K Q 




U B O O TO 


y ra s 


V 03 O O °3 




^fiO O PQ 


fepqo ffl 


J3PQ0 PQ 




^ 










3§ 










3q 













5 66 



APPENDIX. 





ercentage 
Utiliza- 
tion of 
Excess. 








OS 


t^ 








1— 1 


co 








00 


cc 






Hi CO 


CO TjJ 


CO Hi 




»o »o 


■* CO 


t CD 




Ph 












CM 00 

r- <© 


■<* OS 

o >o 


CO Hi 

CO i-H 


30 


CO OS 

1-1 -* 


CO CN 


OS t^ 

00 CO 


<M 

CI 


OS OS 

os o 


ON 

as co 


N CO 
CM N 






J-T 53 o-— 


(O i-t 


Hi ■* 


OS CM 


t^ 


OS CD 


(M CO 


Hi i-H 


•V 


co co 


t^ Tfl 


CN N 


■<** 




«"5 


CO I— 1 


LQ_CO 


c© io^ 


TO 


*1 1 




(M O^ 


°\ 


^ 1 


i—l i-H 


WN 


iO^ 




00* 1 


oo" + 


oo"co* 


of 


Hi ' 


« + 


«Tcm 


CO* 


Hi ' 


«T+ 


icTr-T 


CO* 




a 




























^ 




























c - 


o o 


O 00 


00 CM 


•o 


CM CO 


CD1> 


CO ■<* 


OS 


t^ ^* 


CO i-H 


N Tf 


CO 




m '3 ® 


O OS 


-H 00 


OS o 


OS 


O O 


OS CO 


co r^ 


oo 


i-t os 


CM 00 


O CO 


t>- 




«s e-2 


r- o 


CO ^H 


r- CO 




CO Hi 


t- O 


oo t^ 


- 


Hi CO 


h CM 


"* Hi 


oo 






CD<N 
JO | 


Tj^CD 

Hi + 


O CD 
cO*-h* 


-t* 


Os" | 


co co 
os~ + 


CO^O 

os*'* 




CM --I 

OS" | 


r-t CO 
Os" + 


OS*'** 


co 
>o" 






1-1 


1— 1 FH 






















T3 


b- OS 


IN «5 


CO Hi 




4) O 
"S e ° oi 


i-I CM 


t- O 


OS i-H 




CM O 


CO CO 


-tf CM 




&'oJ cj c5 


00 CM^ 


°1 °V 


CO_^ CO^ 




o S 


■SjT TjT 


co" cm" 


co" co" 




o 


iH <-H 


1— 1 1—1 


i-H 1—1 






t^ 


t~ r-j 


so 


■* CO 


00 OS 


O 


CO .-h 


CM OS 


CO 






• O 


CM CO 


C5 


i>© 


CO I> 


X 


i—l OS 


CM t 


l> 




OS os 


oo co 




OS »o 


•* CO 


3 


o co 


CO I> 


00 


IS 


Tjl O 


CM^ CC 


5 


t^^H 


CO CO 


O 


os ^ 


l> CO 


CO 


| 


a; n CO 


d« 


o" Hi 


■* cm" 1 


cm" t> 


lO* (M* | 


cm" l> 


Hi 


co I 


CO CM 




CM 


(M l-H 




CM 


CM --I 




e 










o 


Average 
Live 

Weight, 
Kgs. 


Hi CO 
OS ** 


00 lO 
l> CD 


l> CD 

rM i-( 




IM 00 


i-H OS 


"* CM 


> 


t> CO 


CD »0 


CO CO 


H 


T3 








a 


_o 


CM r-l 


•«ti CO 


1< CO 


« 


'tH 










fs 








_ 










| 


Q 


pS* P=H fe 


o 




'S 














t« 










!h 










u 
















OS 








0) 








V 














43 








-^> 








-u 




























+3 














"§ -e 






03 +^> 






cd -u 












S 60 






c 60 






d j3 

w 60 










-a ° "s ■ 




rd 2 "53 




■S 2 'S3 










g'd e* 




£"2 |s ; 




C-> — t> 

"3 9 * 










■+3 Slfi s, 
02 t-i £1 




1& g : 




03 °s 










+ 2 "2 








+ o w : 










g* 2 ° § g 

.2 a a -a e 


d =2 a d «- 


:ion 
n fo 

n fo 

ion 
nee. 






ta.2 .2 1 & 


-go o -g a 

03 — i .— 03 t- 


g.S -2^g 






tn -w -u ^ a 


M -S -S K a 


~ +3 +j u as 






• . -2 as as r3 rt 

<J 03 O O 03 


_^ « t) " it 

■•r3 co <u r3 Jt 

03 t_, l^ 03 JT 

■e to E C 2 (2 


sal 
rrec 

rrec 

sal 
Diff 






W 03 o O OS 


u a o o 03 






^eqo o « 


feeqo a pq 


"sPQO O PQ 














t 


=C 










c>2 










CO 













APPENDIX. 



567 



)3 G o 



SO £ ^ 

C Z1 So 

ws a u 



-+ 



coo 
t^ o 



*# o 

O CO 



CO © 
<M O 

00" + 



MH « 
NNp 



(K W O ' 



10 00 


co co 


■* 


10 t~- 


<N H 


co co 


O rH 




C3 + 


cT 1 




'" , 



Tt< IC 



00 02 

CD 03 
O CO 



OJ + 



CM Ol 

id O 
<N rH 

of I 



OS 00 

<N CO 

-# rH 



CM rH 



OS OS 
OS 00 



OS CD 
00 CD 



g-'cJ 03 OS 

o *^ 



o a) >i . 

OJ H gO 



co 00 
CO o 

^* rH 
OS rH 

« + 



00 X 

o ■* 

IO i-H 

<N + 



CO 


O CN 


<M 


t> 00 


00 


<N rH 






■* 


1-1 1 



M if 



w 



w 



Ml 



si 

03 S, 



7? IS 

S3 - J^ 

a p 



o o 



^ 



03 °3 

•2 a 



-^ °J J* 

se s o 






o 
O 



d * 
.2 g 

■a a 
gp 

m 



a 

o h 

P H 



-d 
M 



■a 2 

03 O 

WO 



d cu 

I § 

03 f_ 

03 M 

m 



5 68 



APPENDIX. 



61 i 
c9 c8 l 



On 



>i C3 at 
M-3 -IS n 

Woo 
O 



05 CO 



05 CO 



co co 

CM CO 



O CO 

O rH 

O O 



,-H CO 



Ol CM 
CO tN 



OS t~- 



®2 2.3 



<M O 



<M <# 



OS O 
CO t^ 

©l-H 

00 I 



05 CO 
CO t^ 
GO b- 



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t- + 



CO rt< 

iO 00 

O T»< 



o co 
iO o 



3.S 2.2 
P" e« o3 tS 

0^5 

o 



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if la o~a 
o^.S BO 
S-W 



b- l-H 






fe 



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pq 



p 

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3 S e 
s a o 

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APPENDIX. 



569 



H 
O 

P5 

02 
< 

Eh 

O 

N 

l-H 
tf 

o 

K 
« 

o 

fc 
o 

l-H 

Eh 

o 

s 

O 

u 
o 



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•0 




30 




3 




M 




iC 




rs 


CO 
l-H 






^■- tt i3 2 


OS 


co 





CO 


CM 


os 







00 


00 


os 


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os 


00 


OS 






15 O 


co 





l-H 


OS 


Tfi 


CM 


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■* 


CO 


"5 


1> 


CD 


O 


OS 






CO 
00 


CO 
OS 





OS 

l-H 




os 



CO 

■HH 








co 


10 


OS 


CO 


CO 


OS 


CO 








60 


CO 


(N 


■* 


OS 


CO 





t^ 




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1> 


CO 


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00 


l> 


CO 


CO 


t>- 


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> 




d 

























t^ 


co 


10 


IM 


00 


co 


t^ 




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M ^a 


m 


t> 


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-* 


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l> 


00 


co 




M SP 





00 


CO 


■* 





i> 


os 




m 
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Ph 





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CO 


CO 


T« 


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CO 


CO 


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3) 



















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-> 











co 


t^ 


CO 


1— 1 


CM 


c 


ti 






a> 


10 


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t> 


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CO 


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00 


Ph 




CO 


00 


10 


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CD 
OS 


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th 








00 


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co 


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l> 


10 


co 


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00 


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fc§ u 


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co 


co 


th 


co 


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CO 


co 




Ph. 

















O 








Total 
Heat 
alue of 
xygen, 
cals. 





00 


■* 


os 


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CO 

10 






CM 


00 





10 


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l> 






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00 


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t> 


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co 


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10 


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00 


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00 


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co 


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P.9 




Ph 


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co 


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10 


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3S 






CO 


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co 


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TjH 








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to 
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co 

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00 







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10 


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co 


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co 















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co 


00 


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CN 


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la o.3m 




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00 








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10 






IS 


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OS 


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00 


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t. a m 





to 


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00 








h) 


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10 




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■* 


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10 


















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13 












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fin 

































57o 



APPENDIX. 







m • 




lO 





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00 


on 










00 


CC 


OS 


CM 


■* 






c >»fe 3 S 


OS 


.c 


1—1 


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10 
10 


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00 


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00 


1— 1 
00 













J_l 


CO 


10 


!-H 








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1*3 §S3 


10 


CI 





co 


■* 








1— 1 


1—1 


10 


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00 











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02 

















l-H 




1— i 


1— 1 








b- 


1—1 


CO 


i> 


CO 


t~- 








s 


co 


TfH 


<* 


■* 


b- 


00 








"tf 


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00 


00 


■* 


Tj< 


JO 

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J3 
M 
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M 


O 


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CO 










O 




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O 


01 


^ 


IM 


lO 


H 






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■* 





co 


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6 


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CC 


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b- 


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1 — 1 


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35 

cc 


10 


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1—1 


1 — 1 


1 — 1 


1 — 1 


1 — 1 








O 


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S Z. 




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1 


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Eq 


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co 


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APPENDIX. 



57* 













00 


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t> 


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, 




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10 


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l-H 


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tO 

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ft* 

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co 


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CD 


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3 


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co 


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to 


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t'TS 


CO 


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si 
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0> 


H 


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co 


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10 





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CD 


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co 


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Ph u 


r>. 


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T-H 












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co 












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as 


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05 
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CM 

02 






4) 

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t— 1 


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02 


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t^ 








92 


T-H 


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00 















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, — 1 












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CM 1 


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1 


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10 





to 









Re- 

spira 
tory 
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tient 


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02 






00 


00 


Ol 


00 


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O 

















11 i* rr 


CO 


CN 





10 














CM 


t^ 


T-H 


CO 


CO 








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CD 


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10 


to 






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a) a) 


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co 


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to 


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l> 


00 


10 


10 


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CD 


t^ 


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t^ 


l> 
















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CD 




T3 


u" 


t-J. 


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bC 

tH 


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INDEX. 



PAGE 

Acid, acetic, effect of, on proteid metabolism 123 

total metabolism 160 

replacement value of 160 

aspartic, formed from proteids 39 

oxidized in body 52 

benzoic, formation of hippuric acid from 44 

butyric, effect of, on total metabolism 158 

replacement value of 158 

glutaminic, formed from proteids 39 

hippuric, effect of proteids on formation of 463 

formation of, from benzoic acid 44 

glycocol 44 

in urine 44 

loss of energy in 313, 322 

non-nitrogenous nutrients as source of 45 

origin of 44 

pentose carbohydrates as source of 46 

source of benzoyl radicle of 44, 45 

lactic, effect of, on proteid metabolism 123 

total metabolism 158 

production of, in metabolism of carbohydrates 23 

replacement value of 158 

Acids, organic, absent from excreta 27 

effect of, on proteid metabolism 123 

total metabolism 157 

net available energy of 425 

metabolism of 26 

oxidized in body 27 

produced by fermentation of carbohydrates 13, 26 

replacement values of 157 

Acid, uric, in perspiration 48 

in urine 43 

origin of 43 

573 



574 INDEX. 

PAGE 

Activity, muscular, general features of . . . 185 

Adipose tissue • 29 

Alanine oxidized in body 53 

Albuminoids 7 

compound 7 

composition of 62 

derived 7 

modified 7 

simple 7 

simple, composition of 62 

Albumins 7 

Albumoses formed from proteids 38, 39 

Amido-acids 7 

Amides 7 

formed from proteids 7, 39, 52 

influence of, on digestibility 54 

of carbohydrates 57 

crude fiber 57, 58 

nitrogen-free extract 57 

fermentation of carbohydrates 55 

in digestive tract 54 

metabolism of 52 

not synthesized to proteids 53 

oxidized in body 52 

replacement of proteids by 53 

urea formed from 39 

Ammonium acetate, influence of, on digestibility of carbohydrates. ... 57, 58 

crude fiber 57 

nitrogen-free extract. 57 

carbonate as antecedent of urea 43 

lactate as antecedent of urea 43 

salts influence of, on digestibility of carbohydrates 57 

fermentation of carbohydrates 56 

in digestive tract 56 

in perspiration 48 

Amount of food, critical 408 

influence of, on effects of muscular exertion 197 

net availability of energy 430 

utilization of energy 466 

Anabolism 16, 17 

absorption of energy in 17 

of proteids 38. 41 

Animal, efficiency of 496, 498, 511 

as motor 498 

conditions determining 511 



INDEX. 575 

PAGE 

Animal, efficiency of, influence of fatigue on 519 

gait on 513 

grade on 512 

individuality on 517 

kind of work on 512 

load on 515 

size on 51 5 

species on „ 515 

speed on 513 

training on „ 519 

method of determining 498 

Antecedents of urea 42 

Aromatic compounds in urine 46 

Ascent, work of, in dog, consumption of oxygen in 500 

utilization of energy in 510 

by dog 502 

horse 506 

man 503 

effect of grade on 512 

load on 509,510,515 

Ash ingredients, balance of 79 

Asparagin, influence of, on digestibility 54 

of carbohydrates 57 

crude fiber 57, 58 

nitrogen-free extract 57 

fermentation 54 

of carbohydrates 55 

nutritive value of 54 

oxidized in body 52 

replacement of proteids by 54 

typical of non-proteids 8 

Aspartic acid formed from proteids 39 

oxidized in body 52 

Assimilation, expenditure of energy in digestion and. 372. 375 

tissue building and 491 

of fat, loss of energy in 35 

work of 337, 372,375 

digestion and 80, 93, 406 

above critical point 407 

of bone 381 

carbohydrates 379, 382, 384 

fat 378, 382, 384, 385 

mixed diet 382, 384 

proteids 381, 382, 384 

indirect utilization of heat from. . . . 406 



576 INDEX 



Assimilation, work of, digestion and, in dog 378 

horse 385 

man 382 

methods of determining 377 

relation of, to surface 408 

Availability of energy, gross 270, 395 

for maintenance 396, 406, 410, 413, 427, 497 

work 497 

net 394,412 

net, of energy, determination of 413, 427, 428 

in carnivora 413, 427, 428 

herbivora 418, 427, 428 

distinction between utilization and 395 

of carbohydrates 417, 419, 427, 428 

crude fiber 422, 428 

fat 416, 419, 427, 428 

organic acids 423 

pentoses 420, 428 

proteids 414, 427, 428 

timothy hay 424, 428 

influence of amount of food on 430 

character of food on 431 

relation of maintenance ration to 432 

Barley, utilization of energy of 483, 491 

Beet molasses, metabolizable energy of 293, 297. 301 

digestible protein of 318, 332 

utilization of energy of 483. 490. 491 

Benzoic acid, formation of hippuric acid from 44 

Benzoyl radicle of hippuric acid, source of 44, 45 

Blood, consumption of dextrose of. in muscles 22 

parotid gland 22 

dextrose of 17, 18 

fat production from 23 

percentage of 18 

variations in IS 

fate of dextrose of 22 

lsevulose in 17 

peptones absent from 40 

regulation of supply of dextrose to 1 8, 20 

Body, animal, components of 1 

composition of 60. 64, 66 

conservation of energy in 228, 258 

liberation of energy in 1 

store of energy in 1 

transformations of energy in 2 



INDEX. ST 7 

PAGE 

Body, schematic 60, 66 

Bone, work of digestion and assimilation of 381 

Butyric acid, effect of, on total metabolism 158 

replacement value of 158 

Calorie 232 

Calorimeters, animal 246 

Carbohydrate radicle in proteids 50 

Carbohydrates 8 

apparent digestibility of, influence of amides on 57 

ammonium salts on. 57 

asparagin on 57 

non-proteids on. . . . 57 

as source of energy to body 91 

consumption of, in muscular contraction 220 

digestible, gross energy of 308 

metabolizable energy of 324. 327, 332 

utilization of energy of 475, 477, 490, 491 

disappearance of, in fasting 85 

effects of, on minimum of proteids 135 

proteid metabolism 115 

compared with fat 127 

total metabolism 146 

fermentation of 12, 13 

influence of amides on 55 

ammonium salts on 56 

asparagin on 55 

non-proteids on 55 

on nutritive value 13 

organic acids from 13, 26 

products of 13 

formation of dextrose from, in liver 19, 20, 21 

fat from 24, 30, 165 

equation for 24 

respiratory quotient in 179 

glycogen from 20, 21 

milk fat from. . 174 

hexose 8, 9 

formation of glycogen from 20, 21 

metabolism of. See Metabolism 

resorption of 1 2. 17 

rate of 18 

liver as reservoir of 20 

metabolism of See Metabolism 

mutual replacement of fat and 151 

net available energy of 41 7 419. 427, 428 



57 8 INDEX. 



Carbohydrates, of crude fiber „ 9 

food, replacement of proteids by 149 

nitrogen-free extract 9 

oxidized, computation of, from respiratory quotient 76 

pentose 8, 9 

assimilability of 25 

as source of hippuric acid 46 

determination of 9 

digestibility of 24 

effects of, on proteid metabolism 124 

total metabolism 156 

formation of fat from 183 

glycogen from 25, 26 

metabolism of. See Metabolism 

of crude fiber 9 

nitrogen-free extract 9 

oxidized in body 25 

replacement value of 156 

replacement value of 152 

resorption of 12 

respiratory quotient of 74 

subdivisions of 8, 9 

substitution of, for body fat 146 

utilization of energy of 461, 462, 473, 490, 491 

value of, for maintenance 400,402 

work of digestion and assimilation of 379, 382, 384 

Carbon balance computation of fat from 77 

heat production from nitrogen and 255 

dioxide, determination of, in respiration 69, 73 

produced by fermentation of carbohydrates 13 

production of, in fasting 84 

metabolism 14, 15 

of carbohydrates 23, 27 

fat 36 

proteids 42 

equilibrium, amount of proteids required to produce 105 

factor for computation of fat from 62, 78 

income and outgo of 69 

determination of 69-73 

of excreta, determination of 69 

metabolism, effect of muscular exertion on 209 

Carnivora, determination of net availability of energy in 413, 427, 428 

hippuric acid in urine of . . . 44 

metabolizable energy of food of 272 

utilization of energy by 448, 466 



INDEX. 579 

PAGE 

Cattle, excretion of methane by 243 

Cellulose, effects of, on proteid metabolism 117 

total metabolism 162 

fermentation of 13 

formation of fat from 181 

of crude fiber 9 

replacement value of 162 

Changes, chemical, during muscular contraction 186, 189 

thermal, during muscular contraction 189 

Chymosin 40 

Circulation, effects of muscular exertion on 191 

work of 341 

Cleavage digestive of proteids 38 

purpose of 38 

nitrogen of proteids 98 

cause of 100, 101, 103 

effects of non-nitrogenous nutrients on 131 

independent of total metabolism 99 

of fat in digestion . 12 

proteids in digestion 12, 38 

purpose of 38 

products rebuilding of proteids from 40 

Cleavages, influence of, on computation of Jieat production 253 

by an enzym 40 

Coarse fodders, expenditure of energy of, in digestion, assimilation, and 

tissue building 491 

metabolizable energy of. . . 285, 286, 287, 290, 297, 298, 300, 301 

digestible protein of 320, 332 

carbohydrates of. .327, 332 

non-nitrogenous matter of urine derived from 28 

relative value of grain and, for maintenance 433, 533, 537 

work production 534, 537 

utilization of energy of 484, 490, 491 

Coefficient of utilization of energy 444, 498 

Collagens '. 7 

composition of 62 

Combustion, heats of . 229 

Concentrated feeding-stuffs, metabolizable energy of 289, 297, 299 

digestible protein 

of 315,332 

utilization of energy of .472, 490, 491 

Conservation of energy 228 

in animal body 229, 258 

Contractile substance of muscle 17 

Contraction, muscular 185 



5 8 ° INDEX. 



PAGE 



Contraction, muscular, chemical changes during 186 189 

consumption of carbohydrates in 220 

dextrose in 220, 221 

isometric 495 

isotonic 495 

oxidations in, incomplete 186 

oxygen not essential to 188 

respiratory quotient of muscle in 187 

thermal changes during 189 

transformation of energy in 495 

Creatin. 45 

Creatinin 4g 

in perspiration 48 

Crude fat 8 

fiber g 

apparent digestibility of 12 

influence of amides on 57, 58 

ammonium acetate on . 57 

asparagin on 57, 58 

non-proteids on 57, 58 

carbohydrates of 9 

cellulose of 9 

digestible, gross energy of 303 

metabolizable energy of 329, 332 

digestive work for 389 

effect of, on total metabolism 161 

expenditure of energy of, in digestion, assimilation, and tissue 

building 494 

formation of fat from 181 

f urfuroids of 9 

ligneous material of 9 

modified in digestive tract 12 

net available energy of 422, 428 

pentose carbohydrates of 9 

replacement value of 161 

value of, for maintenance 435, 535, 537 

work production "..... 535, 537 

Descent, work of 509 

influence of grade on 509 

Dextrose, amount of, produced by liver 19 

consumption of, in muscles 221 

muscular contraction 220, 221 

formation of fat from 23 

from carbohydrates in liver 19, 20, 21 

fat 36,385 



INDEX. 5 81 

PAGE 

Dextrose, formation of, from fat during muscular exertion 223 

equation for 38, 51 

in liver 36, 37 

proteids 19, 21, 49, 50 

glycogen from 20, 21, 22 

in muscles 23 

importance of constant supply of 18, 21 

liver as source of 18, 19, 21, 49 

on carbohydrate diet 19 

on proteid diet 19 

method of formation of, in liver 20 

of blood • !7, 18 

consumption of, in muscles 22 

parotid gland 22 

fate of 22 

fat production from 23 

percentage of 1° 

variations in 18 

reconversion of glycogen into 20, 22, 37 

regulation of supply of, to blood 18, 20 

resorption of, rate of 18 

storage of, in resting muscle 222 

Digestibility • ® 

apparent 10, 11 

determination of 10, 11 

influence of metabolic prod- 
ucts on 10 

of carbohydrates, influence of amides on 57, 58 

ammonium salts on 57 
asparagin on. . . . 57, 58 
non-proteids on. 57, 58 

crude fiber 12 

influence of amides on . 57, 58 

ammonium acetate on. 57 

asparagin on 57, 58 

non-proteids on 57 58 

nitrogen-free extract 12 

influence of amides on. . . 57 
ammonium 

acetate on 57 
asparagin on. 57 
non-proteids 

on 57 

significance of results on 11 

determination of 9 



582 INDEX. 

PAGE 

Digestibility, determination of, influence of products of metabolism on. . 10 

of pentose carbohydrates 24 

real 10, 11 

determination of 10 

of fat 10 

protein 10 

Digestion, changes in proteids during 12 

cleavage of fat in 12 

proteids in 12, 38 

purpose of 38 

expenditure of energy in assimilation and 337, 372 

tissue building and. 491 

influence of amides on 54 

asparagin on. 54 

non-proteids on 54 

peptones produced during 12 

proteoses produced during 12 

saponification of fat in 12 

work of 337, 372, 493 

assimilation and 80, 93, 337, 372, 376, 406 

above critical point 407 

below critical point 406 

indirect utilization of heat from. . . . 406 

in the dog 378 

the horse 385 

man 382 

methods of determining 377 

of bone 384 

carbohydrates 379, 382, 384 

fat 378, 382, 384, 385 

mixed diet 382, 384 

proteids 381, 382, 384 

relation of, to surface 408 

factors of 374 

for crude fiber 389 

Digestive tract, functions of, in excretion 10 

Dog, consumption of oxygen by, in locomotion 500 

work of ascent 500 

draft 501 

expenditure of energy by, in locomotion 502 

utilization of energy by, in muscular work. 499 

work of ascent 502 

draft 502 

work of ascent by, consumption of oxygen in 500 

utilization of energy in 502 



INDEX. 5 8 3 

PAGE 

Dog, work of digestion and assimilation in 378 

draft by, consumption of oxygen in 501 

utilization of energy in 502 

Draft, work of, consumption of oxygen in, by dog 501 

horse 507 

utilization of energy in 502, 507, 510, 513 

by dog 502 

horse 507, 510 

Dynamometer for experiments on horses 538, 539 

Dyne 231 

Efficiency of animal. See Animal. 

single muscle 495 

Emission of heat, r ate of, influence of temperature on , . . . . 350 

regulation of 349 

Energy 226 

absorption of, in anabolism 17 

available 269, 394 

gross 270, 395 

net 270, 395 

determination of, in carnivora 413, 427, 428 

herbivora 418, 427, 428 

availability of, distinction between utilization and 395 

for maintenance 396, 406, 410, 413, 427, 497 

influence of amount of food on 430 

character of food on 431 

relation of maintenance ration to 432 

carbohydrates as source of, to body 91 

coefficient of utilization of 440 

conservation of 228 

in animal body 228, 258 

Atwater's and Benedict's inves- 
tigations 265 

early experiments 261 

Laulanie's experiments on. . . . 265 

nature of evidence 259 

Rubner's experiments on 263 

expenditure of, by the body 2, 226, 336, 339 

in digestion and assimilation 372, 375, 376 

and tissue building. 491 
method of deter- 
mining 377 

Energy, expenditure of, in locomotion 510 

by dog 502 

horse, at a trot 509, 510, 514 



5 8 4 INDEX. 



PAGE 



Energy, expenditure of, in locomotion, by horse, at a walk 504, 506, 508, 510 

533, 539 

man 503 

influence of gait on 513 

individuality on 517 

load on 509,510,515 

size of animal on. . . . 516 

species on 516 

speed on 513 

standing 499 

sustaining load 508, 515 

influence of individuality on . . 518 

food as source of 2, 269 

gross, of digestible crude fiber 303 

ether extract 304 

nutrients 302, 306 

organic matter 309 

income and expenditure of 3, 226 

kinetic 226 

determination of „ 245 

liberation of, in animal body 1 

loss of, in assimilation of fat 35 

fermentations 374 

hippuric acid 313, 322 

methane 310, 325, 330, 335 

tissue building 444, 447 

warming ingesta 374 

metabolizable 269, 270 

apparent 291 

factors for 279, 281, 333 

Atwater's 281 

Rubner's 279, 333 

of coarse fodders. 285, 286,287, 290, 297, 298, 300, 301 

concentrated feeding-stuffs 289, 297, 299 

digestible carbohydrates 324, 332 

crude fiber 329, 332 

ether extract 323, 332 

nutrients 310, 332, 333 

organic matter 297, 307 

protein. 310, 315, 317, 318, 320, 327, 332 
fiber-free nutrients, utilization of, in work pro- 
duction 541, 543, 547 

food of carnivora 272 

herbivora 281 

man 277, 280, 282 



INDEX. 5 8 5 

PAGE 

Energy, metabolizable, of nutrients, utilization of, in work production. . . 545 

proteids 272, 276, 277 

total organic matter 284, 285 

real 291 

utilization of, in work production 525, 540 

methods of de- 
termina- 
tion. . . . 526, 528 
Wolff's investi- 
gations 528 

muscular, fat as source of 200, 223 

proteids as source of 201, 207 

source of 196 

starch as source of 199 

nature of demands for 340 

net available 394 

determination of 413, 427, 428 

for maintenance 396, 406, 410, 413, 427, 497 

work 497 

of carbohydrates 417, 419, 427, 428 

crude fiber 422, 428 

fat 416, 419, 427, 428 

organic acids 423 

pentoses 420, 428 

proteids 414, 427, 428 

timothy hay 424, 428 

utilization of, in work 497 

of food .' 2 

protein, losses of, in methane 310 

urine 312 

potential 226 

determination of 235 

of combustible gases 243 

excreta, computation of 241 

determination of 240 

feces, computation of 242 

food, determination of 235 

gain of fat 244 

protein 244 

tissue 244 

perspiration 244 

urine 272, 275, 278, 312 

computation of 241. 277, 312 

store of, in animal body 1 

transformation of, in animal body 2 



586 INDEX. 

PAGE 

Energy, transformation of, in muscular contraction 495 

units of measurement of 231, 233 

utilization of, in tissue building 444, 447, 448, 461 

by carnivora 448, 46G 

man 451 

ruminants 455, 461, 467 

swine. 452, 466 

earlier experiments on 460 

effect of amount of food on 466 

character of food on . . . 472 
differences in live 

weight on 457 

thermal environment on 471 

work 444, 447, 494 

by dog 494 

horse 502 

at a trot 509 

walk 504 

man 502 

influence of fatigue on 519 

individuality on 517 

kind of work on 512 

load on 508 

size of animal on 515 

species on 515 

speed on 507, 513, 514 

training on 519 

of ascent 502, 503, 506, 510 

by dog 502 

horse 506 

man 503 

effect of grade on 512 

load on 509,510,515 

draft 502,510,513 

by dog 502 

horse 507 

locomotion, computed 513 

of barley 483. -191 

beet molasses 483, 490. 491 

carbohydrates 461, 462, 473, 490, 491 

coarse fodders 484, 490, 491 

concentrated feeding-stuffs 472, 490, 491 

digestible carbohydrates 475, 477, 490, 491 

protein 481, 491 

extracted straw 488, 490, 491 



INDEX. 567 



PAGE 



Energy, utilization of, of meadow hay 484, 490, 491 

mixed grains 483, 491 

oat straw 485, 490, 491 

oil 478, 490, 491 

proteids 463, 482, 491 

rice 483, 491 

starch 473, 490, 491 

wheat gluten 480, 490, 491 

straw 487, 490, 491 

Environment, thermal, critical 35S 

influence of, on heat production in fasting 347 

maintenance ration 435 

utilization of energy 471 

Enzym, rebuilding of proteids from cleavage products by 40 

Epidermis, composition of 63 

Ether extract 8 

digestible, gross energy of » . • ■ 304 

metabolizable energy of 323, 332 

Exchange, gaseous, computation of heat production from 249 

effect of load on 509 

muscular exertion on 209 

respiratory, determination of 73 

in fasting 84, 85 

intermediary metabolism 405 

Excreta, determination of carbon of 69 

dioxide in 69 

hydrocarbons in 69, 72 

methane in 69, 72 

hydrogen in 72 

organic acids absent from 27 

percentage of oxygen in 15 

potential energy of, computation of 24 1 

determination of 240 

total, computation of heat production from 252 

Excretion, functions of digestive tract in 10 

nitrogen, ptoteid metabolism and 97 

rate of 98 

effect of non- nitrogenous nutrients on 130 

of free nitrogen. , 42 

methane by cattle 243 

Exertion, muscular (see also Work) . . 185 

effects of, influence of amount of food on 197 

on carbon metabolism 209 

circulation 191 

gaseous exchange 209 



588 INDEX. 

PAGE 

Exertion, muscular, effects of, on metabolism 185, 193 

proteid metabolism 194, 206 

respiration 192 

respiratory quotient 211, 212, 216 

work of heart 192 

formation of dextrose from fat during 223 

functions of proteids in 207 

gain of proteids caused by 204 

general features of 185 

intermediary metabolism during 219 

nature of non-nitrogenous material metabolized in. . 218 

respiratory quotient during, conclusions from 218 

secondary effects of 191 

Expenditure of energy. See Energy. 

Extracted straw, metabolizable energy of 290, 297, 300, 301 

digestible, carbohydrates of . 327, 332 

«. utilization of energy of 488, 490, 491 

Extractives 7 

of muscle 8 

Factor for computation of fat from carbon 62, 78 

non-proteids from nitrogen 8 

protein from nitrogen 67, 68, 77 

Factors for metabolizable energy of digestible nutrients 302, 332, 333 

human food 279, 281 

protein in human foods. 6 

of proteid metabolism in fasting 81, 90 

work of digestion 374 

Fasting, constant loss of tissue in 83 

disappearance of carbohydrates in. 85 

glycogen from liver in 21 

heat production in 344 

constancy of 345 

influence of size of animal on 359 

thermal environment on 347 

is a minimum 347, 356 

measure of internal work 344 

metabolism in 80, 90, 340 

effect of body fat on 88, 90 

loss of protein on 90 

ratio of proteid to total 86, 88, 89, 90, 93 

total 83, 90 

proportional to active tissue 86, 93 

of fat in 85, 88, 90 

proteids in 81, 90 

minimum of proteids less than 136 



INDEX. 589 

PAGE 

Fasting, metabolism of proteids in, tends to become constant 81, 90 

two factors of 81, 90 

minimum of proteids in 82, 83, 90, 94 

oxygen consumption in 84 

production of carbon dioxide in 84 

ratio of fat to protein in body in 88, 89, 90 

respiratory exchange in 84, 85 

Fat 8 

assimilation of, loss of energy in 35 

as source of muscular energy 200, 223 

body, effect of, on fasting metabolism 88, 90 

formation of, from food fat 164 

proteids substituted for 104 

replacement of proteids by 149 

substitution of non-nitrogenous nutrients for 144 

carbohydrates for 146 

fat for 144 

cleavage of, in digestion 12 

composition of, constancy of 35 

from different animals 61 

parts of animal 33 

influence of feeding on 32 

computation of, from carbon balance 77 

crude 8 

deposition of iodine addition products of 31 

digestibility of, real 10 

effects of, on proteid metabolism 114 

compared with carbohydrates. ... 127 

factor for computation of, from carbon 62, 78 

food, formation of body fat from 164 

quantitative relation of, to fat production 34 

replacement of proteids by 149 

foreign, deposition of 30 

formation of dextrose from 23, 385 

during muscular exertion 223 

equation for 38. 51 

in liver 36, 37 

from carbohydrates 24, 30, 165 

equation for 24 

respiratory quotient in 179 

cellulose 181 

crude fiber 181 

dextrose of blood 23 

food fat 164 

non-nitrogenous nutrients of feeding-stuffs 180 



59© INDEX. 

PAGE 

Fat, formation of, from other ingredients of food 163 

pentose carbohydrates 183 

proteids 30, 50, 98, 107 

difficulty of proof 113 

equations for 51 

later experiments Ill 

Pettenkofer and Voit's experiments. . . . 10S 

Pfliiger's recalculations 109 

functions of food 30 

gain or loss of, determination of 69, 77 

influence of glycogen on computation of .. . 66, 78 

potential energy of 244 

influence of, on minimum of proteids 135 

in muscular tissue 63, 64 

katabolism of 35 

loss of energy in assimilation of 35 

manufactured in body 29, 30, 163 

metabolism of. See Metabolism. 

mutual replacement of carbohydrates and 151 

net availability of energy of 416, 419, 427, 428 

of plant, nature of 8 

oxidized, computation of, from respiratory quotient 76 

production, quantitative relation of food fat to 34 

ratio of, to protein in body in fasting 88, 89, 90 

resorption of 12, 30 

respiratory quotient of 74 

saponification of, in digestion 12 

sources of animal 29, 30, 163 

substitution of, for body fat 144 

value of, for maintenance. 400, 402 

work production 522 

work of digestion and assimilation of 378, 382, 384, 385 

Fatigue, influence of, on utilization of energy in work 519 

Fattening, influence of, on maintenance ration 441, 458 

Feces, computation of potential energy of 242 

metabolic nitrogen in 47 

products in 10, 47 

determination of 10 

influence of, on determination of digesti- 
bility 10 

nature of 47 

nitrogenous 42 

Feeding, influence of, on composition of fat 32 

Feeding-stuffs, concentrated, expenditure of energy of, in digestion, assim- 
ilation, and tissue building 492 



INDEX. 591 

PAGE 

Feeding-stuffs, concentrated, metabolizable energy of 289, 297, 299 

digestible protein 

of 315,332 

utilization of energy of 472, 490, 491 

metabolizable energy of, utilization of, in work production 540 
non-nitrogenous nutrients of, effects of, on total metab- 
olism 154 

formation of fat from. ... ISO 
mutual replacement of . . . 154 

non-proteids in 6 

protein in 5 

Fermentation of carbohydrates 12, 13 

influence of amides on 55 

ammonium salts on 50 

asparagin on 55 

non-proteids on 55 

organic acids from 13, 26 

products of 13 

cellulose 13 

Fermentations in digestive tract 12, 13 

influence of amides on 55 

ammonium salts on 56 

asparagin on 54, 55 

non-proteids on 55 

Fermentations, influence of, on nutritive value of carbohydrates 13 

loss of energy in 37-1 

Fiber, crude. See Crude Fiber. 

Flesh bases 8 

Flesh, proteid metabolism expressed in terms of 68 

Food 5 

amount of, critical 408 

influence of, on effects of muscular exertion 197 

net availability of energy 430 

utilization of energy 466 

as source of energy 269 

character of, influence of, on net availability of energy 431 

utilization of energy 472 

composition of ' 5 

digested 12 

consumption, influence of, on heat production. 338, 372, 387 

metabolism 387 

energy of 2 

functions of 3 

fat, functions of 30 



59 2 INDEX. 

PAGE 

Food, increases metabolism 372 

ingredients, heats of combustion of 236 

metabolizable energy of. See Energy. 

nature of 2 

potential energy of, determination of 235 

purposes to which applied 80 

Foods, heats of combustion of 236, 237 

Food-supply, relation of metabolism to 93 

Foot-pound 231 

Force 226 

Furfuroids 9 

of crude fiber „ 9 

nitrogen-free extract 9 

Gain of fat, determination of 69, 77 

influence of glycogen on computation of 66, 78 

potential energy of 244 

nitrogen by body 66, 67 

protein by body 66 

during work 204 

potential energy of 244 

tissue 59 

determination of 60 

potential energy of 244 

Gait, influence of, on expenditure of energy in locomotion. 513 

Gases, combustible, composition of 243 

potential energy of. 243 

Gelatinoids 7 

composition of 62 

Globulin 7 

Glutaminic acid formed from proteids 39 

an intermediate product of proteid metabolism 44 

Glycocol, formation of hippuric acid from 44 

oxidized in body. . 52, 53 

Glycogen, amount of, in body 66, 78 

disappearance of, from liver in fasting 21 

formation of, from artificial hexoses 20 

carbohydrates, hexose 20, 21 

pentose 25, 26 

dextrose 20, 21, 22, 23 

hexoses. . 20, 21 

pentoses 25, 26 

proteids 21, 98 

in liver. 20, 21, 22 

muscles 23 

identical, from different hexoses 20 



INDEX. 593 

PAGE 

Glycogen, identical, from hexoses and pentoses. . . 26 

influence of, on computation of gain or loss of fat 66, 78 

in muscular tissue 64 

muscular, disappearance of, in work 23 

functions of 222, 223 

reappearance of, in rest 23 

reconversion of, into dextrose 20, 22, 37 

Grade, influence of, on efficiency of animal 512 

utilization of energy in work of ascent 512 

work of descent 509 

Grain, relative effects of hay and, on metabolism 388 

value of coarse fodder and, for maintenance 433, 533, 537 

work production 533 

Gram-meter 231 

Gravity, force of 231 

Hair, composition of 63 

Hay, relative effects of grain and, on metabolism 388 

Heart, work of, influence of muscular exertion on 192 

Heat, animal source of 261 

determination of 245 

emission and heat production 256 

influence of insolation on 357 

relative humidity on 358 

wind on 357 

method of, above critical temperature 355 

rate of, influence of temperature on 350 

regulation of 349 

from digestive work, indirect utilization of 406 

production 338 

and heat emission 256 

computation of 249 

from carbon and nitrogen balance .... 255 

gaseous exchange 249 

total excreta 252 

influence of cleavages on 253 

hydrations on 253 

determination of 245 

in fasting 344 

constancy of 345 

influence of size of animal on 359 

thermal environment on 347 

is a measure of internal work 344 

minimum 347, 356 

influence of consumption of food on 338, 372, 387 

water on 438 



594 INDEX. 

PAGE 

Heat production, influence of muscular tonus on 191 

species on 369 

temperature on 351 

thermal environment on 358 

time element on 439 

in intermediary metabolism 405 

on maintenance ration 436, 437 

relation of, to mass of tissue 370 

surface 359 

variations in 351 

causes of 363 

mechanism of 352 

regulation of rate of emission of 349 

Heats of combustion 229 

computation of 239 

of foods " 236, 237 

food ingredients 236, 237 

organic substances 237 

Heat, units of 232 

Hexosans 8 

Hexoses 8 

artificial, formation of glycogen from 20 

formation of glycogen from 20, 21 

Herbivora, determination of net availability of energy in 418, 427, 428 

hippuric acid in urine of 44 

metabolizable energy of food of 281 

minimum of proteids for 140 

Hippuric acid 44 

composition of 44 

formation of, from benzoic acid 44 

glycocol 44 

in urine 44 

loss of energy in 313, 322 

non-nitrogenous nutrients as source of 45 

origin of 44 

pentose carbohydrates as source of 46 

source of benzoyl radicle of 44, 45 

Hoof, composition of 63 

Horn, composition of 63 

Horse, consumption of oxygen in locomotion by 504, 506, 507 

maintenance requirement of 531, 537 

utilization of energy by, in work 502 

at a trot 509 

walk 504 

of ascent 506 



INDEX. 595 

PAGE 

Horse, utilization of energy by, in work, of draft 507 

work of digestion and assimilation in 385 

locomotion in 504, 506, 508, 509, 510, 514, 535, 539 

Human food, metabolizable energy of 277, 280, 282 

foods, protein factors for 6 

Humidity, relative, influence of, on heat emission 358 

Hydrations, influence of, on computation of heat production 253 

Hydrocarbons of excreta, determination of 69, 72 

Hydrogen balance 78 

in excreta 72 

Income and expenditure of energy 3, 226 

matter 3, 5 

Individuality, influence of, on expenditure of energy in locomotion 517 

sustaining load. . . 518 

utilization of energy in work 517 

Indol in urine 46 

Ingesta, warming, loss of energy in 374 

Insolation, influence of, on heat emission 357 

Investigation, methods of 59, 234 

Katabolism 16, 17 

of fat 35 

proteids 41 

excretory nitrogen, measure of 42 

final products of 41 

Keratin, composition of 62 

Kilogram-meter 231 

Kilojoule 231, 232 

Lactic acid, effect of, on proteid metabolism 123 

total metabolism 158 

production of, in metabolism of carbohydrates 23 

replacement value of 158 

Lsevulose in blood 17 

Leucin formed from proteids 39 

oxidized in body 52 

Ligneous material of crude fiber 9 

Liver as reservoir of carbohydrates 20 

source of dextrose 18, 19, 21, 49 

on carboydrate diet 19 

proteid diet 19, 49 

disappearance of glycogen from, in fasting 21 

formation of dextrose in, from carbohydrates 19, 20, 21 

fat 21,36,37 

proteids 19, 21, 45, 50 

method of 20 

glycogen in 20, 21, 22 



59 6 INDEX. 

PAGE 

Liver, formation of glycogen in, from dextrose 20, 21, 22 

proteids 21 

sugar in 18, 19, 21, 49, 50 

functions of 18 

in work production 220 

glycogenic function of 21 

reconversion of glycogen to dextrose in 20, 22, 37 

Live weight, influence of, on maintenance ration. . 458 

utilization of energy 457 

Load, effect of, on expenditure of energy in locomotion. 509, 510, 515 

total metabolism 509, 515 

utilization of energy 508 

in work of ascent. ....... 509, 510, 515 

expenditure of energy in sustaining 508, 515 

influence of individuality on. . . 518 

Locomotion, consumption of oxygen in, by dog 500 

horse 504, 506, 507 

expenditure of energy in 499, 510 

by dog 502 

horse at a trot 509, 510, 514 

walk.. 504, 506, 508, 510, 
533, 539 

man 503 

influence of gait on 513 

individuality on 517 

load on 59, 510, 515 

size of animal on 516 

species on 516 

speed on . .. 507,508, 513 
work of. See Work of Locomotion. 

Loss of fat, determination of 69. 77 

influence of glycogen on computation of 66, 78 

nitrogen by body 66, 67 

protein by body 66 

tissue 59 

constant, in fasting 83 

determination of 60 

Maintenance. 394 

availability of energy for 396, 406, 410, 413, 427, 497 

isodynamic values for 397 

isoglycosic values for 400 

ration 432 

heat production on 436, 437 

of horse 531, 537 

influence of consumption of water on 438 



INDEX. 597 

PAGE 

Maintenance ration, influence of fattening on 441, 458 

live weight on 458 

shearing on. 436 

size of animal on 440 

thermal environment on 435 

time element on 439 

relation of, to net availability of energy 432 

relative value of grain and coarse fodder for 433, 533, 537 

value of carbohydrates for 400-402 

crude fiber 435 

fat for 400, 402 

Man, expenditure of energy by, in locomotion 503 

hippuric acid in urine of 44 

metabolizable energy of food of 277, 280, 282 

utilization of energy by, in muscular work 503 

tissue building 451 

work of ascent 503 

work of digestion and assimilation in 382 

Mastication, work of 391 

Matter, income and expenditure of 3, 5 

Meadow hay, metabolizable energy of 286, 290, 297, 300, 301 

utilization of energy of 484, 490, 491 

Metabolic products, nitrogenous, in feces 42 

Metabolism 14 

a gradual process 16 

an analytic process 15 

a process of oxidation 15 

carbon dioxide produced in 14, 15 

carbon, effects of muscular exertion on 209 

consumption of oxygen in 14, 15, 16 

effects of muscular exertion on 185, 193 

non-nitrogenous nutrients on 114, 125 

proteid supply on 94, 104 

excretory products of 14 

fasting 80, 90, 340 

effect of body fat on 88, 90 

loss of protein on 90 

ratio of proteid to total 81, 88, 89, 90, 93 

total 83, 90 

proportional to active tissue 86, 93 

fat, in fasting 85, 88, 90 

food increases 372 

glandular, similar to muscular 344 

influence of food consumption on 387 

muscular exertion upon. . , 185. 193 



59 8 INDEX. 



PAGE 



Metabolism in muscular tonus 190 

intermediary 91 

during muscular exertion 219 

heat production in 405 

of fat 91 

protein 91 

respiratory exchange in 405 

intermediate products in 16, 44 

muscular, nature of 495 

of amides 52 

carbohydrates 15 17 

hexose 17 

pentose 24 

production of carbon dioxide in 23, 27 

lactic acid in 23 

water in 23, 27 

fat 15 ; 29 

intermediary 91 

production of carbon dioxide in 36 

water in 36 

non-proteids ; 52 

organic acids 26 

proteids 15, 38 

products of, in feces 10, 47- 

determination of 10 

influence of, on determination of diges- 
tibility 10 

nature of 47 

proteid 15, 38 

and nitrogen excretion 97 

determined by supply 128 

effects of acetic acid on 123 

carbohydrates on 115 

compared with fat 127 

cellulose on 117 

excess of proteids on 96 

fat on 114 

compared with carbohydrates 127 

lactic acid on 123 

muscular exertion on 194, 206 

influence of amount 

of food on 197 

non-nitrogenous nutrients on 114, 125 

duration of . . 128 
magnitude of 128 



INDEX. 599 

PAGE 

Metabolism, proteid, effects of organic acids on 123 

pentose carbohydrates on 124 

proteid supply on 94 

starch on 116 

sugars on 116 

expressed in terms of flesh 68 

glycocol intermediate product of 44 

identity of, in different animals 317, 335 

on different feeds 322 

in fasting 81, 90 

minimum of proteids less than 136 

tends to become constant 81,90 

two factors of 81, 90 

intermediate products in 44 

intermediary 91 

production of carbon dioxide in 42 

phosphoric acid in 42 

sulphuric acid in 42 

urea in 42 

water in 42 

ratio of, to total, in fasting 86, 88, 89, 90, 93 

urea as measure of 68 

relations of, to food supply 93 

relative effects of hay and grain on 388 

total, computation of 78 

effect of acetic acid on 160 

butyric acid on 158 

cellulose on 162 

crude fiber on 161 

lactic acid on 1 58 

load on 509, 515 

non-nitrogenous ingredients of feeding-stuffs 

on 154 

nutrients on 144, 154 

organic acids on 157 

pentose carbohydrates on 156 

proteid supply on 104 

rhamnose on 15"' 

in fasting 83, 90 

proportional to active tissue 86, 93 

nitrogen cleavage of proteids independent of 99 

ratio of, to proteid, in fasting 86, 88, 89, 90 

urea produced in 14, 15 

water produced in 14, 15 

Methane, excretion of, by cattle 243 



600 INDEX. 

PAGE 

Methane in excreta, determination of 69, 72 

losses of energy in 310, 325, 328, 330, 335 

produced by fermentation of carbohydrates 13 

Methods of investigation 234 

Milk fat, formation of, from carbohydrates 174 

Minimum demands of vital functions 80 

of proteids 133 

amount of non-nitrogenous nutrients required to 

reach 139 

effect of carboydrates on 136 

fat on 135 

non-nitrogenous nutrients on 134 

on health 143 

for herbivora 140 

in fasting 82, 83, 90, 94 

less than fasting metabolism 136 

Mixed diet, work of digestion and assimilation of 382, 384 

grains, utilization of energy of 483, 491 

Mockern experiments 281, 455 

Motor, efficiency of animal as 498 

Mucins, composition of 62 

Muscle, consumption of dextrose in 22, 221 

contractile substance of 17 

efficiency of single 495 

extractives of 8 

formation of glycogen in 23 

respiratory quotient of 187 

resting, storage of dextrose in 222 

oxygen in 222 

voluntary, work of 337 

Nails, composition of 63 

Nitrogen-free extract, apparent digestibility of 12 

influence of amides on. ... 57 
ammonium 

acetate on. 57 
asparagin on. 57 
non-proteids 

on 57 

carbohydrates of 9 

digestible, gross energy of 305, 306 

furfuroids of 9 

pentose carbohydrates of 9 

Nitrogen balance, computation of heat production from carbon and 255 

cleavage of proteids 98 

cause of 100, 101, 103 



INDEX. 60 1 

PAGE 

Nitrogen cleavage of proteids, effects of non-nitrogenous nutrients on. . . . 131 

independent of total metabolism 99 

content of proteids 39 

equilibrium, amount of proteids required to reach 94 

estimation of protein from 5, 6 

excretion, effect of proteids on 94, 96 

of free 42 

proteid metabolism and 97 

rate of 98 

effects of non-nitrogenous nutrients on 130 

excretory, measure of proteid katabolism 42 

factor for computation of non-proteids from 8 

protein from 67, 68, 77 

gain or loss of, by body 66, 67 

income and outgo of 66 

in perspiration. 48 

metabolic, in feces 47 

percentage of, in body protein 62, 65 

proteids 6, 7 

protein 6, 62, 65 

Non-proteids 7 

asparagin typical of 8 

determination of 8 

factor for computation of, from nitrogen 8 

in feeding-stuffs 6 

influence of, on digestion 54 

apparent digestibility of carbohydrates ... 57 
crude fiber ... 57, 58 
nitrogen-free ex- 
tract 57 

fermentation of carbohydrates 55 

fermentations in digestive tract 54 

of animal body 8 

oxidized in body , 52 

metabolism of 52 

nature of 7 

not synthesized to proteids 53 

produced by cleavage of proteids 7, 8 

replacement of proteids by 53 

resorption of 12 

Nutrients, available 10 

digestible, energy of 302, 306 

gross 302 

metabolizable 310, 332, 333 

factors for 302, 332, 333 



602 INDEX. 

PAGE 

Nutrients, fiber-free, utilization of, in work production 541, 543 

computed 547 

isodynamic replacement of 152 

isoglycosic replacement of 153 

metabolizable energy of, utilization of, in work production .... 545 

modified in digestive tract 12 

mutual replacement of 148 

non-nitrogenous, amount of, required to reach minimum of 

proteids 139 

as source of hippuric acid 45 

effects of, on metabolism 114, 125 

minimum of proteids 134 

nitrogen cleavage of proteids. . . 131 

proteid metabolism 114, 125 

magnitude 

of 12S 

duration of. 128 

rate of nitrogen excretion 130 

total metabolism 144, 154 

formation of fat from 162 

of feeding-stuffs, formation of fat from 180 

mutual replacement of 154 

substitution of, for body fat 144 

utilization of excess of 162 

percentage of oxygen in 5 

relative values of 152 

in work production 522 

replacement values of 152, 396 

Nutrition, function of 2 

statistics of 3 

Oat straw, metabolizable energy of 290, 297, 300 301 

utilization of energy of 485, 490, 491 

Oil, metabolizable energy of 296, 323, 332 

utilization of energy of 478, 490, 491 

Organic acids, absence of, from excreta 27 

net availability of energy of 423 

oxidized in body 27 

matter, digestible, gross energy of 309 

metabolizable energy of 297, 307 

utilization of energy of , 490 

total, metabolizable energy of 284, 285 

utilization of energy of 455,461, 490 

substances, heats of combustion of 237 

Oxidations incomplete in muscular contraction 186 

Oxygen balance 79 



INDEX. 603 

PAGE 

Oxygen, consumption of, determination of 70, 71, 73, 79 

in fasting 84 

locomotion, by dog 500 

horse 504, 506, 507 

metabolism 14, 15, 16 

work of ascent by dog 500 

horse 506 

draft by dog 501 

horse 507 

not essential to muscular contraction 188 

percentage of, in excreta 15 

nutrients 15 

storage of, in resting muscle 222 

Parotid gland, consumption of dextrose of blood in 22 

Peanut oil, metabolizable energy of 296, 323, 332 

Pentosans 8 

oxidized in body 26 

Pentose carbohydrates. See Carbohydrates. 

Pentoses 8 

formation of glycogen from 25, 26 

in urine 25, 26 

metabolism of 24 

net availability of energy of 420, 428 

oxidized in body 25 

Peptones absent from blood 40 

formed from proteids 12, 38, 39 

produced during digestion 12 

synthesis of, to proteids by an enzym 40 

Perspiration, ammonium salts in 48 

creatinin in 48 

nitrogen in 48 

nitrogenous matter in 42 

potential energy of 242 

proteids in 48 

urea in 48 

uric acid in 48 

Phenols in urine 27, 46 

Phosphoric acid, production of, in metabolism of proteids 42 

Phosphorus balance 79 

Plastein , 40 

Proteids 6 

albumoses formed from 38, 39 

amides formed from 7, 39, 52 

not synthesized to 53 



604 INDEX. 



PAGE 



Proteids, amount of, required to produce carbon equilibrium. . 105 

nitrogen equilibrium 94 

anabolism of 38, 41 

aspartic acid formed from 39 

as source of muscular energy 201, 207 

body, and food proteids 40 

carbohydrate radicle in 50 

changes in, during digestion 12 

classification of 7 

cleavage of, in digestion 12, 38 

purpose of 38 

non-proteids produced by 7, 8 

differences in 39 

effect of excess of, on proteid metabolism 96 

on formation of hippuric acid 463 

metabolism 94, 104 

nitrogen excretion 94, 96 

proteid metabolism 94 

total metabolism 104 

food, and body proteids 40 

formation of dextrose from, in liver 19, 21, 49, 50 

fat from 30, 50, 98, 101 

difficulty of proof of 113 

equations for 51 

later experiments Ill 

Pettenkofer and Voit's experiments. . . . 108 

Pfliiger's recalculations 109 

glycogen from 21 , 98 

sugar from 19, 21, 49, 50 

functions of, in muscular exertion 207 

gain of, during work 204 

glutaminic acid formed from 39 

in perspiration 48 

intermediary metabolism of 91 

katabolism of 41 

excretory nitrogen measure of 42 

final products of 41 

leucin formed from 39 

metabolizable energy of 272, 276, 277 

metabolism of. See Metabolism. 

minimum of 133 

amount of non-nitrogenous nutrients required to 

reach 139 

effect of non-nitrogenous nutrients on 134 

effects of, on health 143 



INDEX. 605 



PAGE 



Proteids, minimum of, for herbivora 140 

in fasting 82, 83, 90, 94 

influence of carbohydrates on 136 

fat on 135 

less than proteid metabolism in fasting 136 

molecular weight of 15 

nature of 39 

net availability of energy of 414, 427, 428 

nitrogen cleavage of 98 

cause of 100, 101, 103 

effects of non-nitrogenous nutrients on. . . . 131 

independent of total metabolism 97 

content of 6, 7, 39 

non-nitrogenous residue of 48, 98 

fate of 49, 98 

formation of sugar from 49, 50, 98 

non-proteids not synthesized to 53 

peptones formed from 12, 38, 39 

percentage of nitrogen in 6, 7 

proteoses formed from 12, 39 

putrefaction of, in intestines 44, 46 

products of 44, 46 

rebuilding of, from cleavage products 40 

replacement of, by amides 53 

asparagin 54 

body fat 149 

fats and carbohydrates of food 149 

non-proteids 53 

resorption of 12 

respiratory quotient of 74, 75 

synthesis of peptones to 40 

substituted for body fat 104 

Proteid supply, effects of, on metabolism 94, 104 

proteid metabolism : 94 

total metabolism 104 

Proteids, terminology of 5, 7 

transitory storage of 96 

tyrosin formed from 39 

utilization of energy of 482, 491 

excess of 107 

work of digestion and assimilation of 381, 382, 384 

Protein, circulatory 82 

composition of 62 

digestibility of, real 10 

digestible, gross energy of • 309 



606 INDEX, 

PAGE 

Protein, digestible, metabolizable energy of . . 310, 315, 317, 318, 320, 327, 332 

utilization of energy of 481, 491 

estimation of, errors in 6 

from nitrogen 5, 6 

factor for computation of, from nitrogen 6, 67, 68, 77 

in human foods 6 

gain or loss of, by body 66 

potential energy of 244 

in feeding-stuffs 5 

loss of, in fasting, effect of, on metabolism 90 

energy of, in methane 310 

urine 312 

nature of 5 

of body, composition of 62, 65, 66 

percentage of nitrogen in 62, 65 

organized 82 

percentage of nitrogen in 6, 62, 65 

ratio of fat to, in body in fasting 88, 89, 90 

real digestibility of 10 

storage, cause of 102 

extent of 132 

terminology of 6, 7 

Proteoses, formed from proteids 8, 12, 39 

produced during digestion 12 

Putrefaction of proteids in intestines 44, 46 

products of 44, 46 

Quotient, respiratory 74 

change in, caused by work 212 

computation from, of carbohydrates oxidized 76 

fat oxidized 76 

deductions from 75 

during work, conclusions from 75 

effects of muscular exertion on 211 

in fat-formation from carbohydrates 179 

of carbohydrates 74 

fat 74 

muscle 187 

influence of contraction on 187 

proteids 74, 75 

variations of 211 

during work 216 

Range, thermic 348 

Rate of nitrogen excretion 98 

Ration, maintenance. See Maintenance. 

Regulation of body temperature 347, 348 



INDEX. 607 

page 

Regulation of body temperature, chemical 352 

means of 348 

physical 351 

emission of heat 349 

Rennet ferment, functions of 40, 41 

Replacement, isodynamic, law of 152, 399 

isoglycosic, law of 153, 399 

mutual, of fat and carbohydrates 151 

non-nitrogenous ingredients of feeding-stuffs. . . 154 

nutrients 148 

of proteids by amides 53 

asparagin 54 

body fat 149 

carbohydrates and fat of food 149 

non-proteids 53 

value of acetic acid 160 

butyric acid 158 

carbohydrates 152 

cellulose 162 

crude fiber 161 

lactic acid 158 

non-nitrogenous ingredients of feeding-stuffs 154 

nutrients 152 

organic acids 157 

pentose carbohydrates 156 

rhamnose 156 

Residue, non-nitrogenous, of proteids 48, 98 

fate of 49, 98 

formation of sugar from 49, 50, 98 

Resorption of carbohydrates 12 

hexose 12, 17 

rate of 18 

dextrose, rate of 18 

fat 12, 30 

non-proteids 12 

proteids 12 

Respiration apparatus 69 

determination of water by 79 

Pettenkofer type of 70 

Regnault type of 69 

Zuntz type of 72 

Respiration-calorimeter 246, 248 

Respiration, determination of products of 69, 73 

effects of muscular exertion on 192 

work of 193, 341 



608 INDEX. 

PAGE 

Respiratory exchange, determination of 73 

in intermediary metabolism 405 

Rest, reappearance of muscular glycogen in 23 

Rhamnose, effect of, on total metabolism 156 

replacement value of 156 

Rice, utilization of energy of 483, 491 

Ruminants, utilization of energy in 455, 461, 467 

Sarkosin oxidized in body „ 53 

Saponification of fat in digestion 12 

Schematic body „ 60, 66 

Shearing, influence of, on maintenance ration 436 

Size of animal, influence of, on efficiency of animal 515 

expenditure of energy in locomotion 516 

heat production 359 

in fasting 359 

maintenance ration 440 

relation of, to physiological activities 368 

Species, comparison of heat production of 369 

influence of, on efficiency of animal 515 

expenditure of energy in locomotion 511 

Speed, correction for, in work of locomotion 507, 508 

influence of, on expenditure of energy in locomotion 507, 508, 513 

utilization of energy in work 507, 513, 514 

Standing, expenditure of energy in 343, 499 

Starch, as source of muscular energy 199 

digestible, gross energy of 306 

metabolizable energy of 324, 332 

utilization of energy of 475, 477, 490 

effect of, on proteid metabolism 116 

metabolizable energy of 294, 297, 301 

utilization of energy of 473, 490, 491 

States, initial and final, law of 228 

Statistics of nutrition 3 

Storage of protein, extent of 132 

transitory 96 

cause of 102 

Straw, extracted, gross energy of carbohydrates of 308 

metabolizable energy of 290, 297, 300, 301 

carbohydrates of 327 

utilization of energy of 488, 490, 491 

oat, metabolizable energy of 290, 297, 300, 301 

protein of 321 

carbohydrates of ,. 329 

utilization of energy of 485, 490, 49 1 

wheat, metabolizable energy of 290, 297, 300, 301 



INDEX 609 

PAGE 

Straw, wheat, metabolizable energy of protein of 321 

carbohydrates 329 

utilization of energy of 487, 490, 491 

Sugar, effect of, on proteid metabolism 116 

formation of, from non-nitrogenous residue of proteids 49, 50, 98 

proteids 19, 21, 49, 50 

in liver 18, 19, 21, 49, 50 

Sulphur balance 79 

Sulphuric acid, conjugated, in urine 46 

production of, in metabolism of proteids 42 

Surface of animal, computation of 364 

relation of heat production to 359 

internal work to 366 

to work of digestion and assimilation ...... 408 

Swine, utilization of energy by 452, 466 

Temperature, body 347 

regulation of 347, 348 

chemical 352 

means of 348 

physical 351 

critical 353 

method of heat emission above 355 

modification of conception of 357 

influence of, on heat production 351 

rate of emission of heat 350 

Thermal environment, critical 358 

influence of, on heat production in fasting 347 

maintenance ration 435 

utilization of energy 471 

Thermic range 348 

Thermo-chemistry 228 

Time element, influence of, on heat production 439 

maintenance ration 439 

Timothy hay, metabolizable energy of 287, 290, 297, 301 

net availablity of energy of 424, 428 

Tissue 59 

active, fasting metabolism proportional to 86, 93 

adipose . 29 

building, expenditure of energy in digestion, assimilation, and ... 491 

loss of energy in 444, 447 

utilization of energy in 444, 447, 448, 461 

by carnivora 448, 466 

man 451 

ruminants 455, 461, 467 

swine 452, 466 



6io INDEX. 



PAGE 



Tissue, building, utilization of energy in, earlier experiments on 460 

effect of amount of food on ... . 466 
character of food on . . . 472 
differences in live weight 

on 457 

thermal environment on 471 

constant loss of, in fasting 83 

gain of potential energy in 244 

gains and losses of 59 

determination of 60 

mass of, relation of heat production to 370 

muscular, composition of 63, 64 

fat in 63, 64 

glycogen in 64 

heat of combustion of 63, 64 

Tonus, muscular 190 

influence of, on heat production 191 

metabolism in 190 

work of 341 

Training, influence of, on utilization of energy in work 519 

Transformation of energy in body 2 

muscular contraction 495 

Trot, expenditure of energy in locomotion at 509, 510, 514 

utilization of energy in work at 509 510 

Tyrosin, formed from proteids 39 

oxidized in body 52 

Units of heat 232 

measurement of energy 231, 233 

Urea ; 42 

antecedent of 42 

ammonium carbonate as 43 

lactate as 43 

as measure of proteid metabolism 68 

in perspiration 48 

production of, from amides 52 

in metabolism 14, 15 

of proteids 42 

Uric acid 43 

origin of 43 

in perspiration 48 

urine 43 

Urine, aromatic compounds in „ 46 

computation of potential energy of 241, 313 

conjugated sulphuric acid in 46 



INDEX. 611 

PAGE 

Urine, hippuric acid in 44 

indol in 46 

losses of energy of protein in 312 

non-nitrogenous matter of 27, 312, 320 

amount of 28 

derived from coarse fodders 28 

non-nitrogenous matter. . 321 

influence of 320 

source of 27, 321 

pentoses in 25, 26 

phenols in 27, 46 

potential energy of 272, 275, 278, 312 

computation of 241, 277, 312 

uric acid in 43 

Utilization of energy. See Energy. 

Values, isodynamic 397, 399 

isoglycosic 399, 400 

replacement 396 

modified conception of 405 

of nutrients 396 

Variations in heat production, causes of 363 

Walking, consumption of oxygen in, by horse 505 

expenditure of energy in, by horse 504, 506, 508, 510, 533, 539 

utilization of energy in, by horse 513 

Water, consumption of, influence of, on heat production 438 

maintenance ration 438 

determination of, by respiration apparatus 79 

production of, in metabolism 14, 15 

of carbohydrates 23, 27 

fat 36 

proteids 42 

Wheat gluten, digestible protein of, metabolizable energy of 310, 317 

gross energy of 309 

utilization of energy of 481, 491 

metabolizable energy of 295, 297, 301 

digestible matter of ; . . . 301 

utilization of energy of 480, 490, 491 

straw, digestible carbohydrates of, metabolizable energy of 329 

crude fiber of, metabolizable energy of 330, 332 

matter of, gross energy of 310 

metabolizable energy of , . . 300, 301 

utilization of energy of 487 

protein of, metabolizable energy of 321, 332 

metabolizable energy of 290, 297, 300, 301 



612 INDEX. 

PAGE 

Wheat straw, utilization of energy of 461, 487, 490, 491 

Wind, influence of, on heat emission 357 

Wool, composition of 63 

Work. (See also Exertion, muscular) 226 

cellular 344 

change in respiratory quotient caused by 212 

coefficient of utilization in „ 498 

disappearance of muscular glycogen in 23 

gain of proteids during 204 

glandular 343 

internal 336, 337 

fasting heat production a measure of 344 

muscular 341 

relation of, to surface 366 

kind of, influence of, on efficiency of animal 512 

mechanical, determination of 245 

muscular, disappearance of glycogen in 23 

incidental 342 

net available energy for 497 

of ascent, consumption of oxygen in, by dog 500 

corrected 508 

utilization of energy in 502, 503, 510 

by dog 502 

horse 506 

man 503 

effect of grade on 512 

load on 509, 510 

circulation 191, 341 

descent 509 

influence of grade on 509 

digestion and assimilation 80, 93, 337, 372, 376, 406, 493 

above critical point 407 

below critical point 406 

indirect utilization of heat from. . . . 406 

in dog 378 

horse 385 

man. . 382 

methods of determining 377 

of bone 381 

carbohydrates 379, 382, 384 

fat 378, 382, 384, 385 

mixed diet 382. 384 

proteids 381, 382, 384 

relation of, to surface. 408 



INDEX. 613 

PAGE 

Work of digestion, factors of 374 

for crude fiber 389 

draft, consumption of oxygen in, by dog 501 

utilization of energy in 502, 507, 513 

by dog 502 

horse 507, 513 

heart 192, 341 

locomotion, computation of 512 

consumption of oxygen in, by dog. 500 

horse 505 

correction for speed in 507, 508 

expenditure of energy in, by dog 500 

horse 504, 506, 508, 509 

510, 514, 533, 539 

utilization of energy in, computed 513 

mastication 391 

muscular tonus 341 

respiration 192, 341 

standing 343 

voluntary muscles 337 

physiological 336 

production, function of liver in 206 

relative value of nutrients in 522 

coarse fodder and grain 

for 533 

value of crude fiber for 535, 537 

fat for 522 

utilization of energy in 444, 447, 494 

by dog 499 

horse 502 

at a trot 509 

walk 504 

man 502 

influence of fatigue on 519 

individuality on 517 

kind of work on 512 

load on 508 

size of animal on 515 

species on 515 

speed on 507, 513, 514 

training on 519 

jnetabolizable energy in 525 

methods of determina- 
tion 526, 528 



6 14 INDEX. 

PAGE 

Work, utilization of metabolizable energy in, Wolff's investigations 528 

of feeding-stuffs in 540 

fiber-free nutrients in 541, 543, 
545, 547 

net available energy in 497 

variations of respiratory quotient during 216 



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Bernadou's Smokeless Powder. — Nitro-cellulose, and Theory of 

the Cellulose Molecule 12mo, 2 50 

Bolton's Quantitative Analysis 8vo, 1 50 

Brush and Penfield's Manual of Determinative Mineralogy...8vo, 4 00 
Classen's Quantitative Chemical Analysis by Electrolysis. (Her- 

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Cohn's Indicators and Test-papers 12mo, 2 00 

Craft's Short Course in Qualitative Chemical Analysis. (Schaef- 

fer.) 12mo, 2 00 

Drechsel's Chemical Reactions. (Merrill.) 12mo, 1 25 

Eissler's Modern High Explosives 8vo, 4 00 

Effront's Enzymes and their Applications. (Prescott.) . . . .8vo, 3 00 
Erdmann's Introduction to Chemical Preparations. (Dunlap.) 

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Fletcher's Practical Instructions in Quantitative Assaying with 

the Blowpipe 12mo, morocco, 1 50 

Fowler's Sewage Works Analyses 12mo, 2 00 

Fresenius's Manual of Qualitative Chemical Analvsis. (Wells.) Svo, 5 00 
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Analysis. (Allen.) 8vo, 6 00 



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Fuertes's Water and Puniic Health 12mo, 

Furman's Manual of Practical Assaying 8vo, 

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Hopkins's Oil-chemists' Handbook 8vo, 

Keep's Cast Iron 8vo, 

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Mandel's Handbook for Bio-chemical Laboratory 12mo, 1 50 

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Meyer's Determination of Radicles in Carbon Compounds. 

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Richards's Cost of Living as Modified by Sanitary Science 12mo, 100 
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Stockbridge's Rocks and Soils 8vo, 2 50 

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Johnson's Theory and Practice of Surveying Small 8vo, 4 00 

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Kiersted's Sewage Disposal 12mo, 1 25 

Laplace's Philosophical Essav on Probabilities. CTruscott and 

Emory.) 12mo, 2 00 

Mahan's Treatise on Civil Engineering. (1873.) (Wood.) . .8vo, 5 00 

* Mahan's Descriptive Geometry 8vo, 1 50 

Merriman's Elements of Precise Surveying and Geodesy. .. .8vo, 2 50 

Merriman and Brooks's Handbook for Surveyors. . . .16mo, mor., 2 00 

Merriman's Elements of Sanitary Engineering 8vo, 2 00 

Nugent's Plane Surveying 8vo, 3 50 

Ogden's Sewer Design 12mo, 2 00 

Patton's Treatise on Civil Engineering 8vo, half leather, 7 50 

Reed's Topographical Drawing and Sketching 4to, 5 00 

Rideal's Sewage and the Bacterial Purification of Sewage. . . 8vo, 3 50 

Siebert and Biggin's Modern Stone-cutting and Masonry. . . .8vo, 1 50 

Smith's Manual of Topographical Drawing. (McMillan.) . .8vo, 2 50 

•Trautwine's Civil Engineer's Pocket-book. .. .16mo, morocco, 5 00 

Wait's Engineering and Architectural Jurisprudence 8vo, 6 00 

Sheep, 6 50 
" Law of Operations Preliminary to Construction in En- 
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Sheep, 5 50 

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Warren's Stereotomy — Problems in Stone-cutting 8vo, 2 50 

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Instruments 16mo, morocco, 1 25 

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Du Bois's Mechanics of Engineering. Vol. II Small 4to, 10 00 

Foster's Treatise on Wooden Trestle Bridges 4to, 5 00 

Fowler's Coffer-dam Process for Piers Svo, 2 50 

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" Specifications for Steel Bridges 12mo, 1 25 

Wood's Treatise on the Theory of the Construction of Bridges 

and Roofs 8vo, 2 00 

Wright's Designing of Draw-spans: 

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Church's Mechanics of Engineering 8vo, 

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paper, 
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Folwell's Water-supply Engineering. 8vo, 

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Riveted, Metal Conduits ... .8vo, 2 00 

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Mason's Water-supply. (Considered Principally from a Sani- 
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Merriman's Treatise on Hydraulics 8vo, 4 00 

* Michie's Elements of Analytical Mechanics 8vo, 4 00 

Schuyler's Reservoirs for Irrigation, Water-power, and Domestic 

Water-supply Large 8vo, 5 00 

Turneaure and Russell. Public Water-supplies 8vo, 5 00 

Wegmann's Design and Construction of Dams 4to, 5 00 

" Water-supply of the City of New York from 1658 to 

1895 4to, 10 00 

Weisbach's Hydraulics and Hydraulic Motors. (Du Bols.) . .8vo, 5 00 

Wilson's Manual of Irrigation Engineering Small 8vo, 4 00 

Wolff's Windmill as a Prime Mover 8vo, 3 08 

Wood's Turbines. 8vo, 2 60 

" Elements of Analytical Mechanics 8vo, 3 00 



MATERIALS OF ENGINEERING. 

Baker's Treatise on Masonry Construction 8vo, 5 00 

Black's United States Public Works Oblong 4to, 5 00 

Bovey's Strength of Materials and Theory of Structures. . . .8vo, 7 50 
Burr's Elasticity and Resistance of the Materials of Engineer- 
ing ,..8vo, 5 00 

Byrne's Highway Construction 8vo, 5 00 

" Inspection of the Materials and Workmanship Em- 
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Church's Mechanics of Engineering. 8vo, 6 00 

Du Bois's Mechanics of Engineering. Vol. I Small 4to, 7 50 

Johnson's Materials of Construction. Large Kvo, 6 00 

Keep's Cast Iron 8vo, 2 50 

Lanza's Applied Mechanics 8vo, 7 5© 

Martens's Handbook on Testing Materials. (Henning.).2 v., 8vo, 7 50 

Merrill's Stones for Building and Decoration 8vo, 5 00 

Merriman's Text-book on the Mechanics of Materials 8vo, 4 00 

Merriman's Strength of Materials 12mo, 1 00 

Metcalf s Steel. A Manual for Steel-users. 12mo, 2 00 

Patton's Practical Treatise on Foundations 8vo, 5 00 

Rockwell's Roads and Pavements in France 12mo, 1 25 

Smith's Wire: Its Use and Manufacture Small 4to, 3 00 

" Materials of Machines 12mo, 1 00 

Snow's Principal Species of Wood: Their Characteristic Proper- 
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Spalding's Hydraulic Cement 12mo, 2 00 

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Thurston's Materials of Engineering 3 Parts, 8vo, 8 00 

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and Their Constituents 8vo, 2 50 

Thurston's Text-book of the Materials of Construction 8vo, 5 00 

Tillson's Street Pavements and Paving Materials 8vo, 4 00 

Waddell's De Pontibus. (A Pocket-book for Bridge Engineers.) 

16mo, morocco, 3 00 

" Specifications for Steel Bridges 12mo, 1 25 

Wood's Treatise on the Resistance of Materials, and an Ap- 
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" Elements of Analytical Mechanics 8vo, 3 00 

7 



RAILWAY ENGINEERING. 

uidrews's Handbook for Street Railway [Engineers. 3x5 in. mor., 1 25 

Jerg's Buildings and Structures of American Railroads. . .4to, 5 00 

Brooks's Handbook of Street Railroad Location.. 16mo, morocco, 1 50 

Butts's Civil Engineer's Field-book 16mo, morocco, 2 50 

Crandall's Transition Curve 16mo, morocco, 1 50 

Railway and Other Earthwork Tables ..8vo, 1 50 

Dawson's Electric Railways and Tramways. Small 4to, half mor., 12 50 
" " Engineering " and Electric Traction Pocket-book. 

16mo, morocco, 4 00 

Dredge's History of the Pennsylvania Railroad : (1879.) .Paper, 5 00 

* Drinker's Tunneling, Explosive Compounds, and Rock Drills. 

4to, half morocco, 25 00 

Fisher's Table of Cubic Yards. Cardboard, 25 

Godwin's Railroad Engineers' Field-book and Explorers' Guide. 

16mo, morocco, 2 50 

Howard's Transition Curve Field-book 16mo, morocco, 1 50 

Hudson's Tables for Calculating the Cubic Contents of Exca- 
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Nagle's Field Manual for Railroad Engineers 16mo, morocco, 3 00 

Philbrick's Field Manual for Engineers ...16mo, morocco, 3 00 

Pratt and Alden's Street-railway Road-bed 8vo, 2 00 

Searles's Field Engineering. 16mo, morocco, 3 00 

" Railroad Spiral 16mo, morocco, 1 50 

Taylor's Prismoidal Formulae and Earthwork . 8vo, 1 50 

* Ttautwine's Method of Calculating the Cubic Contents of Ex- 

cavations and Embankments by the Aid of Dia- 
grams 8vo, 2 00 

* The Field Practice of Laying Out Circular Curves 

for Railroads ... 12mo, morocco, 2 50 

* Cross-section Sheet. Paper, 25 

Webb's Railroad Construction. 8vo, 4 00 

Wellington's Economic Theory of the Location of Railways. . 

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DRAWING. 

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Coolidge's Manual of Drawing 8vo, paper, 1 00 

Durley's Elementary Text-book of the Kinematics of Machines. 

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Hill's Text-book on Shades and Shadows, and Perspective. . 8vo, 2 00 
Jones's Machine Design: 

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Part n. — Form, Strength and Proportions of Parts . .8vo, 3 00 

MacCord's Elements of Descriptive Geometry 8vo, 3 00 

Kinematics ; or, Practical Mechanism 8vo, 5 00 

Mechanical Drawing 4to, 4 00 

Velocity Diagrams 8vo, 1 50 

* Mahan's Descriptive Geometry and Stone-cutting. ..... .8vo, 1 50 

Mahan's Industrial Drawing. (Thompson.) 8vo, 3 50 

Reed's Topographical Drawing and Sketching .4to, 5 00 

Reid's Course in Mechanical Drawing. 8vo, 2 00 

" Text-book of Mechanical Drawing and Elementary Ma- 
chine Design 8vo, 3 00 

Robinson's Principles of Mechanism 8vo, 3 00 



Smith's Manual of Topographical Drawing. (McMillan.) .8vo, 2 50 
Warren's Elements of Plane and Solid Free-hand Geometrical 

Drawing 12mo, 1 00 

" Drafting Instruments and Operations 12mo, 1 25 

" Manual of Elementary Projection Drawing. .. .12mo, 1 50 
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" Primary Geometry 12mo, 75 

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Geometry 8vo, 2 50 

Weisbaeh's Kinematics and the Power of Transmission. (Herr- 
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Whelpley's Practical Instruction in the Art of Letter En- 
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Wilson's Topographic Surveying 8vo, 3 50 

Wilson's Free-hand Perspective 8vo, 2 50 

Woolf's Elementary Course in Descriptive Geometry. .Large 8vo, 3 00 



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Small 8vo, 3 00 
Anthony's Lecture-notes on the Theory of Electrical Measur- 

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Benjamin's History of Electricity 8vo, 3 00 

Benjamin's Voltaic Cell 8vo, 3 00 

Classen's Qantitative Chemical Analysis by Electrolysis. Her- 

rick and Boltwood.) 8vo, 3 00 

Crehore and Squier's Polarizing Photo-chronograph 8vo, 3 00 

Dawson's Electric Railways and Tram ways.. Small 4to, half mor., 12 50 
Dawson's " Engineering " and Electric Traction Pocket-book. 

16mo, morocco, 4 00 

Flather's Dynamometers, and the Measurement of Power. . 12mo, 3 00 

Gilbert's De Magnete. (Mottelay.) 8vo, 2 50 

Holman's Precision of Measurements 8vo, 2 00 

Telescopic Mirror-scale Method, Adjustments, and 

Tests Large 8vo, 75 

Landauer's Spectrum Analysis. (Tingle.) 8vo, 3 00 

Le Chatelier's High- temperature Measurements. (Boudouard — 

Burgess.) 12mo, 3 00 

LSb's Electrolysis and Electrosynthesis of Organic Compounds. 

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Lyons's Treatise on Electromagnetic Phenomena 8vo, 6 00 

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* Tillman. Elementary Lessons in Heat 8vo, 1 50 

Tory and Pitcher. Manual of Laboratory Physics. .Small 8vo, 2 00 

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LAW. 

* Davis. Elements of Law 8vo, 2 50 

Treatise on the Military Law of United States. .8vo, 7 00 

Sheep, 7 50 

Manual for Courts-martial 16mo, morocco, 1 50 

Wait's Engineering and Architectural Jurisprudence 8vo, 6 00 

Sheep, 6 60 
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Sheep, 5 50 

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Winthrop's Abridgment of Military Law.... 12mo, 2 5® 

MANUFACTURES. 

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Bernadou's Smokeless Powder — Nitro-cellulose and Theory of 

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Bolland's Iron Founder 12mo, cloth, 2 50 

" " The Iron Founder " Supplement 12mo, 2 50 

" Encyclopedia of Founding and Dictionary of Foundry 

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Eissler's Modern High Explosives. 8vo, 4 00 

Effront's Enzymes and their Applications. (Prescott.).. .8vo, 3 00 

Fitzgerald's Boston Machinist 18mo. 1 00 

Ford's Boiler Making for Boiler Makers 18mo, 1 00 

Hopkins's Oil-chemists' Handbook 8vo, 3 00 

Keep's Cast Iron 8vo 2 50 

Leach's The Inspection and Analysis of Food with Special 
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Metcalf's Steel. A Manual for Steel-users 12mo, 2 00 

Metcalf's Cost of Manufactures — And the .administration of 

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Meyer's Modern Locomotive Construction 4to 

* Reisig's Guide to Piece-dyeing 8vo 

Smith's Press- working of Metals 8vo 

" Wire: Its Use and Manufacture Small 4to 

Spalding's Hydraulic Cement 12mo 

Spencer's Handbook for Chemists of Beet-sugar Houses. 

16mo, morocco 
Handbook for Sugar Manufacturers and their Chem- 
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Thurston's Manual of Steam-boilers, their Designs, Construc- 
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Walke's Lectures on Explosives 8vo 

West's American Foundry Practice 12mo 

" Moulder's Text-book 12mo 

Wiechmann's Sugar Analysis Small 8vo 

Wolff's Windmill as a Prime Mover 8vo 

Woodbury's Fire Protection of Mills 8vo 



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MATHEMATICS. 



Baker's Elliptic Functions 8vo, 1 60 

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Briggs's Elements of Plane Analytic Geometry 12mo, 1 00 

Chapman's Elementary Course in Theory of Equations. . .12mo, 1 50 

Compton's Manual of Logarithmic Computations 12mo, 1 50 

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Davis's Introduction to the Logic of Algebra 8vo, 

•Dickson's College Algebra Large 12mo, 

Halsted's Elements of Geometry 8vo, 

" Elementary Synthetic Geometry. 8vo, 

•Johnson's Three-place Logarithmic Tables: Vest-pocket size, 

pap., 
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10 copies for 
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Small 8vo, 

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Treatise on Ordinary and Partial Differential 

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* " Theoretical Mechanics „ ... 12mo, 

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Emory.) " 12mo, 2 00 

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Merriman and Woodward. Higher Mathematics 8vo, 5 00 

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Rice and Johnson's Elementary Treatise on the Differential 

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MATERIALS OF ENGINEERING, STEAM ENGINES 
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Baldwin's Steam Heating for Buildings 12mo, 2 60 

Barr's Kinematics of Machinery 8vo, 2 50 

* Bartlett's Mechanical Drawing 8vo, 3 00 

Benjamin's Wrinkles and Recipes 12mo, 2 00 

Carpenter's Experimental Engineering 8vo, 6 00 

" Heating and Ventilating Buildings 8vo, 4 00 

Clerk's Gas and Oil Engine Small 8vo, 4 00 

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Cromwell's Treatise on Toothed Gearing 12mo, 1 60 

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Durley's Elementary Text-book of the Kinematics of Machines. 

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Flather's Dynamometers, and the Measurement of Power . . 12mo, 3 00 

" Rope Driving.. 12mo, 2 00 

Gill's Gas an Fuel Analysis for Engineers 12mo, 1 25 

Hall's Car Lubrication l2mo, 1 00 

Jones's Machine Design: 

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Kent's Mechanical Engineers' Pocket-book. .. .16mo, morocco, 5 00 

Kerr's Power and Power Transmission 8vo, 2 00 

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MacCord's Kinematics ; or, Practical Mechanism 8vo, 

Mechanical Drawing 4to, 

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Mahan's Industrial Drawing. (Thompson.) .8vo, 

Poole's Calorific Power of Fuels 8vo, 

Reid's Course in Mechanical Drawing. 8vo, 

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Machine Design 8vo, 

Richards's Compressed Air . 12mo, 

Robinson's Principles of Mechanism 8vo, 

Smith's Press-working of Metals 8vo, 

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Animal as a Machine and Prime Motor and the 

Laws of Energetics 12mo, 

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" Hydraulics and Hydraulic Motors. (Du Bois.) .8vo, 

Wolff's Windmill as a Prime Mover 8vo, 

Wood's Turbines. 8vo, 

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Bovey's Strength of Materials and Theory of Structures. .8vo, 7 50 
Burr's Elasticity and Resistance of the Materials of Engineer- 
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Church's Mechanics of Engineering 8vo, 6 00 

Johnson's Materials of Construction Large 8vo, 6 00 

Keep's Cast Iron 8vo, 2 50 

Lanza's Applied Mechanics .8vo, 7 50 

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Thurston's Text-book of the Materials of Construction .... 8vo, 5 00 
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" Elements of Analytical Mechanics 8vo, 3 00 

STEAM ENGINES AND BOILERS. 

Carnot's Reflections on the Motive Power of Heat. (Thurston.) 

12mo, 1 50 
Dawson's " Engineering " and Electric Traction Pocket-book. 

16mo, morocco, 4 00 

Ford's Boiler Making for Boiler Makers 18mo, 1 00 

Goss's Locomotive Sparks 8vo, 2 00 

Hemenway's Indicator Practice and Steam-engine Economy- 

12mo, 2 00 

Hutton's Mechanical Engineering of Power Plants 8vo, 5 00 

" Heat and Heat-engines 8vo, 5 00 

12 



Kent's Steam-boiler Economy 8vo, 4 00 

Kneass's Practice and Theory of the Injector 8vo, 1 50 

MacCord's Slide-valves 8vo, 2 00 

Meyer's Modern Locomotive Construction. . . . 4to, 10 00 

Peabody's Manual of the Steam-engine Indicator 12mo, 1 50 

Tables of the Properties of Saturated Steam and 

Other Vapors 8vo, 1 00 

" Thermodynamics of the Steam-engine and Other 

Heat-engines 8vo, 5 00 

Valve-gears for Steam-engines. . 8vo, 2 50 

Peabody and Miller. Steam-boilers 8vo, 4 00 

Pray's Twenty Years with the Indicator Large 8vo, 2 50 

Pupin's Thermodynamics of Reversible Cycles in Gases and 

Saturated Vapors. (Osterberg.) 12mo, 1 25 

Reagan's Locomotive Mechanism and Engineering 12mo, 2 00 

Rontgen's Principles of Thermodynamics. (Du Bois.) . . . .8vo, 5 00 

Sinclair's Locomotive Engine Running and Management. .12mo, 2 00 

Smart's Handbook of Engineering Laboratory Practice. .12mo, 2 50 

Snow's Steam-boiler Practice 8vo, 3 00 

Spangler's Valve-gears 8vo, 2 50 

" Notes on Thermodynamics 12mo, 1 00 

Thurston's Handy Tables 8vo, 1 50 

" Manual of the Steam-engine. » 2 vols., 8vo, 10 00 

Part I. — History, Structure, and Theory 8vo, 6 00 

Part II. — Design, Construction, and Operation 8vo, 6 00 

Thurston's Handbook of Engine and Boiler Trials, and the Use 

of the Indicator and the Prony Brake .8vo, 5 00 

" Stationary Steam-engines 8vo, 2 50 

" Steam-boiler Explosions in Theory and in Prac- 
tice 12mo, 1 50 

" Manual of Steam-boilers, Their Designs, Construc- 
tion, and Operation 8vo, 5 00 

Weisbach's Heat, Steam, and Steam-engines. (Du Bois.)..8vo, 5 00 

Whitham's Steam-engine Design „ 8vo, 5 00 

Wilson's Treatise on Steam-boilers- (Flather.) 16mo, 2 50 

Wood's Thermodynamics, Heat Motors, and Refrigerating 

Machines 8vo, 4 00 

MECHANICS AND MACHINERY. 

Barr's Kinematics of Machinery 8vo, 2 50 

Bovey's Strength of Materials and Theory of Structures. .8vo, 7 50 

Chordal. — Extracts from Letters 12mo, 2 00 

Church's Mechanics of Engineering 8vo, 6 00 

" Notes and Examples in Mechanics 8vo, 2 00 

Compton's First Lessons in Metal-working 12mo, 1 50 

Compton and De Groodt. The Rpped Lathe. 12mo, 1 50 

Cromwell's Treatise on Toothed Gearing 12m o, 1 50 

Treatise on Belts and Pulleys 12mo, 1 50 

Dana's Text-book of Elementary Mechanics for the Use of 

Colleges and Schools 12mo, 1 50 

Dingey's Machinery Pattern Making 12mo, 2 00 

Dredge's Record of the Transportation Exhibits Building of the 

World's Columbian Exposition of 1893 4to, half mor., 5 00 

Du Bois's Elementary Principles of Mechanics: 

Vol. I. — Kinematics 8vo, 3 50 

Vol. II.— Statics 8vo, 4 00 

Vol. III.— Kinetics 8vo, 3 50 

Du Bois's Mechanics of Engineering. Vol. I Small 4to, 7 50 

Vol.11 Small 4to, 10 00 

13 



Dun-ley's Elementary Text- book of the Kinematics of Machines. 

(In preparation.) 

Fitzgerald's Boston Machinist. 16mo, 1 00 

Flather's Dynamometers, and the Measurement of Power . 12mo, 3 00 

" Rope Driving 12mo, 2 00 

Goss's Locomotive Sparks 8vo, 2 00 

Hall's Car Lubrication 12mo, 1 00 

Holly's Art of Saw Filing 18mo, 75 

* Johnson's Theoretical Mechanics 12mo, 3 00 

Johnson's Short Course in Statics by Graphic and Algebraic 

Methods. (In preparation.) 
Jones's Machine Design: 

Part I. — Kinematics of Machinery 8vo, 1 50 

Part II. — Form, Strength and Proportions of Parts. .. .8vo, 3 00 

Kerr's Power and Power Transmission 8vo, 2 00 

Lanza's Applied Mechanics 8vo, 7 50 

MaeCord's Kinematics; or, Practical Mechanism ..8vo, 5 00 

" Velocity Diagrams 8vo, 1 50 

Merriman's Text-book on the Mechanics of Materials 8vo, 4 00 

* Michie's Elements of Analytical Mechanics 8vo, 4 00 

Reagan's Locomotive Mechanism and Engineering. 12mo, 2 00 

Reid's Course in Mechanical Drawing 8vo, 2 00 

" Text-book of Mechanical Drawing and Elementary 

Machine Design 8vo, 3 00 

Riehards's Compressed Air 12mo, 1 50 

Robinson's Principles of Mechanism 8vo, 3 00 

Ryan, Norris, and Hoxie's Electrical Machinery. (In preparation.) 

Sinclair's Locomotive-engine Running and Management. .12mo, 2 00 

Smith's Press-working of Metals 8vo, 3 00 

" Materials of Machines 12mo, 1 00 

Thurston's Treatise on Friction and Lost Work in Machin- 
ery and Mill Work. 8vo, 3 00 

" Animal as a Machine and Prime Motor, and the 

Laws of Energetics. 12mo, 1 00 

Warren's Elements of Machine Construction and Drawing. .8vo, 7 50 
Weisbach's Kinematics and the Power of Transmission. 

(Herrman — Klein.) 8vo, 5 00 

" Machinery of Transmission and Governors. (Herr- 

(man — Klein.) 8vo, 5 00 

Wood's Elements of Analytical Mechanics .8vo, 3 00 

" Principles of Elementary Mechanics. 12mo, 1 25 

" Turbines 8vo, 2 50 

The World's Columbian Exposition of 1893 4to, 1 00 

METALLURGY. 

Egleston's Metallurgy of Silver, Gold, and Mercury: 

Vol. I.-Silver 8vo, 7 50 

Vol. II. — Gold and Mercury 8vo, 7 50 

** Ees's Lead-smelting 12mo, 2 50 

Keep's Cast Iron 8vo, 2 50 

Kunhardt's Practice of Ore Dressing in Iurope. 8vo, 1 50 

Le Chatelier's High-temperature Measurements. (Boudouard — 

Burgess.) 12mo, 3 00 

Metcalf's Steel. A Manual for Steel-users 12mo, 2 00 

Smith's Materials of Machines 12mo, 4 00 

Thurston's Materials of Engineering. In Three Parts 8vo, 8 00 

Part II.— Iron and Steel 8vo, 3 50 

Part HI. — A Treatise on Brasses, Bronzes and Other Alloys 

and Their Constituents 8vo, 2 50 

14 



MINERALOGY. 

Barringer's Description of Minerals of Commercial Value. 

Oblong, morocco, 2 50 

Boyd's Resources of Southwest Virginia 8vo, 3 00 

" Map of Southwest Virginia Pocket-book form, 2 00 

Brush's Manual of Determinative Mineralogy. (Penfield.) .8vo, 4 00 

Chester's Catalogue of Minerals 8vo, paper, 1 00 

Cloth, 1 25 

Dictionary of the Names of Minerals 8vo, 3 50 

Dana's System of Mineralogy Large 8vo, half leather, 12 50 

" First Appendix to Dana's New " System of Mineralogy." 

Large 8vo, 1 00 

" Text-book of Mineralogy 8vo, 4 00 

" Minerals and How to Study Them 12mo, 1 50 

" Catalogue of American Localities of Minerals . Large 8vo, 1 00 

" Manual of Mineralogy and Petrography 12mo, 2 00 

Egleston's Catalogue of Minerals and Synonyms 8vo, 2 50 

Hussak's The Determination of Rock-forming Minerals. 

(Smith.) Small 8vo, 2 00 

•Penfield's Notes on Determinative Mineralogy and Record of 

Mineral Tests 8vo, paper, 50 

Rosenbuseh's Microscopical Physiography of the Rock-making 

Minerals. (Idding's.) 8vo, 5 00 

•Tillman's Text- book of Important Minerals and Rocks.. 8 vo, 2 00 

Williams's Manual of Lithology 8vo, 3 00 



MINING. 

Beard's Ventilation of Mines 12mo, 2 50 

Boyd's Resources of Southwest Virginia 8vo, 3 00 

" Map of Southwest Virginia Pocket-book form, 2 00 

•Drinker's Tunneling, Explosive Compounds, and Rock 

Drills 4to, half morocco, 25 00 

Eissler's Modern High Explosives 8vo, 4 00 

Fowler's Sewage Works Analyses 12mo, 2 00 

Goodyear's Coal-mines of the Western Coast of the United 

States 12mo, 2 50 

Dilseng's Manual of Mining . . ... 8vo, 4 00 

** Hes's Lead-smelting 12mo, 2 50 

Kunhardt's Practice of Ore Dressing in Europe 8vo, 1 50 

O'Driscoll's Notes on the Treatment of Gold Ores. 8vo, 2 00 

Sawyer's Accidents in Mines 8vo, 7 00 

Walke's Lectures on Explosives 8vo, 4 00 

Wilson's Cyanide Processes 12mo, 1 50 

Wilson's Chlorination Process 12mo, 1 50 

Wilson's Hydraulic and Placer Mining 12mo, 2 00 

Wilson's Treatise on Practical and Theoretical Mine Ventila- 
tion 12mo, 1 25 

SANITARY SCIENCE. 

Folwell's Sewerage. (Designing, Construction and Maintenance.) 

8vo, 3 00 

" Water-supply Engineering 8vo, 4 00 

Fuertes's Water and Public Health 12mo, 1 60 

" Water-filtration Works 12mo, 2 50 

15 



Gerhard's Guide to Sanitary House-inspection 16mo, 1 00 

Goodrich's Economical Disposal of Towns' Refuse. . .Demy 8vo, 3 50 

Hazen'a Filtration of Public Water-supplies 8vo, 3 00 

Kiersted's Sewage Disposal 12mo, 1 25 

Leach's The Inspection and Analysis of Food with Special 

Reference to State Control. (In preparation.) 
Mason's Water-supply. (Considered Principally from a San- 
itary Standpoint. 3d Edition, Rewritten 8vo, 4 00 

" Examination of Water. (Chemical and Bacterio- 
logical.) 12mo, 1 25 

Merriman's Elements of Sanitary Engineering 8vo, 2 00 

Nichols's Water-supply. (Considered Mainly from a Chemical 

and Sanitary Standpoint.) (1883.) 8vo, 2 50 

Ogden's Sewer Design 12mo, 2 00 

* Price's Handbook on Sanitation. 12mo, 1 50 

Richards's Cost of Food. A Study in Dietaries 12mo, 1 00 

Richards and Woodman's Air, Water, and Food from a Sani- 
tary Standpoint 8vo, 2 00 

Richards's Cost of Living as Modified by Sanitary Science . 12mo, 1 00 

* Richards and Williams's The Dietary Computer Svo, 1 50 

Rideal's Sewage and Bacterial Purification of Sewage 8vo, 3 50 

Turneaure and Russell's Public Water-supplies. .-. .8vo, 5 00 

Whipple's Microscopy of Drinking-water 8vo, 3 50 

Woodhull's Notes on Military Hygiene 16mo, 1 50 



MISCELLANEOUS. 

Barker's Deep-sea Soundings 8vo, 2 00 

Emmoixs's Geological Guide-book of the Rocky Mountain Ex- 
cursion of the International Congress of Geologists. 

Large 8vo, 1 50 

Ferrel's Popular Treatise on the Winds 8vo, 4 00 

Haines's American Railway Management 12mo, 2 50 

Mott'a Composition, Digestibility, and Nutritive Value of Food. 

Mounted chart, 1 25 

" Fallacy of the Present Theory of Sound. 16mo, 1 00 

Ricketts's History of Rensselaer Polytechnic Institute, 1824- 

1894 Small 8vo, 3 00 

Rotherham'a Emphasised New Testament. . . Large 8vo, 2 00 

" Critical Emphasised New Testament 12mo, 1 50 

Steel's Treatise on the Diseases of the Dog. 8vo, 3 50 

Totten's Important Question in Metrology. .............. .8vo, 2 50 

The World's Columbian Exposition of 1893 4to, 1 00 

Worcester and Atkinson. Small Hospitals, Establishment and 
Maintenance, and Suggestions for Hospital Architecture, 

with Plans for a Small Hospital 12mo, 1 25 



HEBREW AND CHALDEE TEXT-BOOKS. 

Green's Grammar of the Hebrew Language 8vo, 3 00 

" Elementary Hebrew Grammar 12mo, 1 25 

" Hebrew Chrestomathy 8vo, 2 00 

Gesenius's Hebrew and Chaldee Lexicon to the Old Testament 

Scriptures. (Tregelles.) Small 4to, half morocco, 5 00 

Letteris's Hebrew Bible 8vo, 2 25 

16 



l-tlj 2 1903 



LIBRARY OF CONGRESS 



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